Method and apparatus for transreceiving downlink signal by considering antenna  port relationship in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system, and more specifically, disclosed are a method and an apparatus for transmitting or receiving a downlink signal by considering an antenna port relationship. A method for user equipment decoding an enhanced physical downlink control channel (EPDCCH) in the wireless communication system, according to one embodiment of the present invention, comprises the steps of: determining a quasi co-location (QCL) of an antenna port of the EPDCCH; and decoding the EPDCCH based on the QCL with respect to the antenna port of the EPDCCH. The user equipment can determine a QCL assumption between an antenna port of an EPDCCH demodulation reference signal and an antenna port of a different reference signal based on the type of a QCL assumption with respect to a PDSCH.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting orreceiving a downlink signal by considering an antenna port relationship.

BACKGROUND ART

Multiple-Input Multiple-Output (MIMO) technology is a technology forimproving efficiency of data transmission and reception using multipletransmit antennas and multiple receive antennas rather than using onetransmit antenna and one receive antenna. If a single antenna is used, areceive entity receives data through a single antenna path. In contrast,if multiple antennas are used, the receive entity receives data throughseveral paths, accordingly data transmission rate and throughput may beimproved, and the coverage may be extended.

To increase multiplexing gain of the MIMO operation, an MIMO transmitentity may use channel state information (CSI) fed back by the MIMOreceive entity. The receive entity may determine the CSI by performingchannel measurement using a predetermined reference signal (RS) from thetransmit entity.

DISCLOSURE Technical Problem

In an advanced wireless communication system, a relationship betweendifferent antenna ports may be defined in various manners. For example,a terminal may assume that different RS ports of a network are quasico-located (QCL) or that that the RS ports are not QCL, without askingwhether the different RS ports are present at the same location.

An object of the present invention devised to solve the problem lies ina method for a terminal to accurately and efficiently receive a downlinksignal transmitted from the network side by considering a relationship(particularly, a QCL relationship) between antenna ports.

It is to be understood that technical objects to be achieved by thepresent invention are not limited to the aforementioned technicalobjects and other technical objects which are not mentioned herein willbe apparent from the following description to one of ordinary skill inthe art to which the present invention pertains.

Technical Solution

The object of the present invention can be achieved by providing amethod for decoding an enhanced physical downlink control channel(EPDCCH) by a user equipment (UE) in a wireless communication system,the method including determining quasi co-location (QCL) regarding anantenna port for the EPDCCH, and decoding the EPDCCH based on the QCLregarding the antenna port for the EPDCCH. When a first assumption thatan antenna port for a cell-specific reference signal (CRS), an antennaport for a UE-specific reference signal (RS) for a physical downlinkshared channel (PDSCH), and an antenna port for a channel stateinformation-RS (CSI-RS) are quasi co-located (QCL) is applied, theEPDCCH may be decoded on an assumption that the antenna port for the CRSand an antenna port for a demodulation RS (DMRS) for the EPDCCH arequasi co-located.

In another aspect of the present invention, provided herein is a userequipment (UE) for decoding an enhanced physical downlink controlchannel (EPDCCH) in a wireless communication system, the UE including atransmit module, a receive module, and a processor. The processor may beconfigured to determine quasi co-location (QCL) regarding an antennaport for the EPDCCH and to decode the EPDCCH based on the QCL regardingthe antenna port for the EPDCCH, When a first assumption that an antennaport for a cell-specific reference signal (CRS), an antenna port for aUE-specific reference signal (RS) for a physical downlink shared channel(PDSCH), and an antenna port for a channel state information-RS (CSI-RS)are quasi co-located (QCL) is applied, the EPDCCH may be decoded on anassumption that the antenna port for the CRS and an antenna port for ademodulation RS (DMRS) for the EPDCCH are quasi co-located.

The above aspects of the present invention may include the followingdetails in common.

Application of the first assumption may include configuring, by a higherlayer, the UE such that the UE performs decoding of the EPDCCH based onthe first assumption.

When a second assumption that the antenna port for the UE-specific RSfor the PDSCH and an antenna port for a specific CSI-RS are quasico-located is applied, the EPDCCH may be decoded on an assumption thatthe antenna port for the specific CSI-RS and the antenna port for theDMRS for the EPDCCH are quasi co-located.

Application of the second assumption may include configuring, by ahigher layer, the UE such that the UE performs decoding of the PDSCHbased on the second assumption.

When the second assumption is applied, the specific CSI-RS may be anon-zero power (NZP) CSI-RS configured by a higher layer.

When one antenna port and another antenna port are quasi co-located,large-scale properties of the one antenna port may be inferred fromlarge-scale properties of the other antenna port.

The large scale properties may include at least one of delay spread,Doppler spread, Doppler shift and average delay.

At least one EPDCCH-physical resource block (PRB)-set for monitoring theEPDCCH may be configured for the UE. A parameter set for each of the atleast one EPDCCH-PRB-set may be indicated by a higher layer. Thedetermining may be performed based on the parameter set indicated by thehigher layer.

The parameter set indicated by the higher layer may be a specific PQI(PDSCH resource element mapping and Quasi co-location Indicator)parameter set. The specific PQI parameter set may be used for thedecoding of the EPDCCH.

The parameter set may include at least one of parameters correspondingto number-of-CRS ports information, CRS frequency shift information,Multicast Broadcast Single Frequency Network (MBSFN) subframeconfiguration information, zero power (ZP) CSI-RS configurationinformation, a PDSCH start symbol value, and non-zero power (NZP) CSI-RSconfiguration information.

A PDSCH signal may be received based on downlink control information(DCI) received through the EPDCCH.

The UE may be set to transmission mode 10 (TM10).

The above general description and the following detailed description ofthe present invention are exemplarily given to supplement therecitations in the claims.

Advantageous Effects

According to embodiments of the present invention, a terminal mayaccurately and efficiently receive a downlink signal transmitted fromthe network side by considering a relationship (particularly, a QCLrelationship) between antenna ports.

It will be appreciated by those skilled in the art that the effects thatcan be achieved with the present invention are not limited to what hasbeen described above and other advantages of the present invention willbe clearly understood from the following detailed description taken inconjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a radio frame structure;

FIG. 2 is a diagram illustrating a resource grid for one downlink (DL)slot;

FIG. 3 is a diagram illustrating a DL subframe structure;

FIG. 4 is a diagram illustrating an uplink (UL) subframe structure;

FIG. 5 illustrates configuration of a wireless communication systemhaving multiple antennas;

FIG. 6 is a diagram illustrating an exemplary pattern of a CRS and a DRSon one RB pair;

FIG. 7 is a diagram illustrating an exemplary DMRS pattern defined inLTE-A;

FIG. 8 is a diagram illustrating exemplary CSI-RS patterns defined inLTE-A;

FIG. 9 is a diagram illustrating an exemplary scheme in which a CSI-RSis periodically transmitted;

FIG. 10 illustrates carrier aggregation;

FIG. 11 is a diagram illustrating cross-carrier scheduling;

FIG. 12 is a flowchart illustrating a method for transmitting andreceiving a EPDCCH signal according to one embodiment of the presentinvention;

FIG. 13 is a diagram illustrating configurations of a base station and auser equipment.

BEST MODE

The embodiments described below are constructed by combining elementsand features of the present invention in a predetermined form. Theelements or features may be considered selective unless explicitlymentioned otherwise. Each of the elements or features can be implementedwithout being combined with other elements. In addition, some elementsand/or features may be combined to configure an embodiment of thepresent invention. The sequence of the operations discussed in theembodiments of the present invention may be changed. Some elements orfeatures of one embodiment may also be included in another embodiment,or may be replaced by corresponding elements or features of anotherembodiment.

Embodiments of the present invention will be described focusing on adata communication relationship between a base station and a terminal.The base station serves as a terminal node of a network over which thebase station directly communicates with the terminal. Specificoperations illustrated as being conducted by the base station in thisspecification may be conducted by an upper node of the base station, asnecessary.

In other words, it will be obvious that various operations allowing forcommunication with the terminal in a network composed of several networknodes including the base station can be conducted by the base station ornetwork nodes other than the base station. The term “base station (BS)”may be replaced with terms such as “fixed station,” “Node-B,” “eNode-B(eNB),” and “access point (AP),” “remote radio head (RRD),”“transmission point (TP),” and “reception point (RP).” The term “relay”may be replaced with terms such as “relay node (RN)” and “relay station(RS)”. The term “terminal” may also be replaced with such terms as “userequipment (UE),” “mobile station (MS),” “mobile subscriber station(MSS)” and “subscriber station (SS).”

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and these specific terms may bechanged to other formats within the technical scope or spirit of thepresent invention.

In some cases, known structures and devices may be omitted or blockdiagrams illustrating only key functions of the structures and devicesmay be provided, so as not to obscure the concept of the presentinvention. The same reference numbers will be used throughout thisspecification to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments for at least one of wireless access systems including aninstitute of electrical and electronics engineers (IEEE) 802 system, a3rd generation partnership project (3GPP) system, a 3GPP long termevolution (LTE) system, an LTE-advanced (LTE-A) system, and a 3GPP2system. In particular, steps or parts, which are not described in theembodiments of the present invention to prevent obscuring the technicalspirit of the present invention, may be supported by the abovedocuments. All terms used herein may be supported by the above-mentioneddocuments.

The embodiments of the present invention described below can be appliedto a variety of wireless access technologies such as code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), and single carrier frequency division multiple access(SC-FDMA). CDMA may be embodied through wireless technologies such asuniversal terrestrial radio access (UTRA) or CDMA2000. TDMA may beembodied through wireless technologies such as global system for mobilecommunication (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). OFDMA may be embodied through wirelesstechnologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, and evolved UTRA (E-UTRA). UTRA is a part of universal mobiletelecommunications system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS),which uses E-UTRA. 3GPP LTE employs OFDMA for downlink and employsSC-FDMA for uplink. LTE-Advanced (LTE-A) is an evolved version of 3GPPLTE. WiMAX can be explained by IEEE 802.16e (wirelessMAN-OFDMA referencesystem) and IEEE 802.16m advanced (wirelessMAN-OFDMA advanced system).For clarity, the following description focuses on 3GPP LTE and 3GPPLTE-A systems. However, the spirit of the present invention is notlimited thereto.

FIG. 1 illustrates a radio frame structure.

In a cellular OFDM wireless packet communication system, an uplink(UL)/downlink (DL) data packet is transmitted on a subframe-by-subframebasis, and one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. 3GPP LTE supports a type-1 radioframe structure applicable to frequency division duplex (FDD) and atype-2 radio frame structure applicable to time division duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into ten subframes. Each subframe includes two slots inthe time domain. The time taken to transmit one subframe is defined as atransmission time interval (TTI). For example, a subframe may have aduration of 1 ms and one slot may have a duration of 0.5 ms. A slot mayinclude a plurality of OFDM symbols in the time domain and a pluralityof resource blocks (RBs) in the frequency domain. Since 3GPP LTE employsOFDMA for downlink, an OFDM symbol represents one symbol period. An OFDMsymbol may be referred to as an SC-FDMA symbol or a symbol period. Aresource block (RB), which is a resource allocation unit, may include aplurality of consecutive subcarriers in a slot.

The number of OFDM symbols included in one slot depends on theconfiguration of a cyclic prefix (CP). CPs are divided into an extendedCP and a normal CP. For a normal CP configuring each OFDM symbol, a slotmay include 7 OFDM symbols. For an extended CP configuring each OFDMsymbol, the duration of each OFDM symbol is extended and thus the numberof OFDM symbols included in a slot is smaller than in the case of thenormal CP. For the extended CP, a slot may include, for example, 6 OFDMsymbols. When a channel status is unstable as in the case of high speedmovement of a UE, the extended CP may be used to reduce inter-symbolinterference.

When the normal CP is used, each slot includes 7 OFDM symbols, and thuseach subframe includes 14 OFDM symbols. In this case, the first two orthree OFDM symbols of each subframe may be allocated to a physicaldownlink control channel (PDCCH) and the other three OFDM symbols may beallocated to a physical downlink shared channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. The type-2 radioframe includes two half frames, each of which includes 5 subframes, adownlink pilot time slot (DwPTS), a guard period (GP), and an uplinkpilot time slot (UpPTS). One subframe includes two slots. A subframeincluding a DwPTS, a GP and a UpPTS may be referred to as a specialsubframe. The DwPTS is used for initial cell search, synchronization, orchannel estimation in a UE, whereas the UpPTS is used for channelestimation in an eNB and UL transmission synchronization in a UE. The GPis provided to eliminate interference on UL caused by multipath delay ofa DL signal between DL and UL. Regardless of the type of a radio frame,a subframe of the radio frame includes two slots.

The illustrated radio frame structures are merely examples, and variousmodifications may be made to the number of subframes included in a radioframe, the number of slots included in a subframe, or the number ofsymbols included in a slot.

FIG. 2 is a diagram illustrating a resource grid for one DL slot.

A DL slot includes 7 OFDM symbols in the time domain and an RB includes12 subcarriers in the frequency domain. However, embodiments of thepresent invention are not limited thereto. For a normal CP, a slot mayinclude 7 OFDM symbols. For an extended CP, a slot may include 6 OFDMsymbols. Each element in the resource grid is referred to as a resourceelement (RE). An RB includes 12×7 REs. The number NDL of RBs included ina downlink slot depends on a DL transmission bandwidth. A UL slot mayhave the same structure as a DL slot.

FIG. 3 illustrates a DL subframe structure.

Up to first three OFDM symbols of the first slot in a DL subframecorrespond to a control region to which control channels are allocatedand the other OFDM symbols of the DL subframe corresponds to a dataregion to which a physical downlink shared channel (PDSCH) is allocated.

DL control channels used in 3GPP LTE include, for example, a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), and a physical hybrid automatic repeat request (HARQ)indicator channel (PHICH). The PCFICH is transmitted in the first OFDMsymbol of a subframe, carrying information about the number of OFDMsymbols used for transmission of control channels in the subframe. ThePHICH carries a HARQ ACK/NACK signal in response to uplink transmission.Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI includes UL or DL scheduling information orUL transmit power control commands for UE groups. The PDCCH deliversinformation about resource allocation and a transport format for a DLshared channel (DL-SCH), resource allocation information about a ULshared channel (UL-SCH), paging information of a paging channel (PCH),system information on the DL-SCH, information about resource allocationfor a higher-layer control message such as a random access responsetransmitted on the PDSCH, a set of transmit power control commands forindividual UEs of a UE group, transmit power control information, andvoice over internet protocol (VoIP) activation information. A pluralityof PDCCHs may be transmitted in the control region, and a UE may monitorPDCCHs.

A PDCCH is formed by aggregating one or more consecutive control channelelements (CCEs). A CCE is a logical allocation unit used to provide aPDCCH at a coding rate based on the state of a radio channel. A CCEcorresponds to a plurality of RE groups. The format of a PDCCH and thenumber of available bits for the PDCCH are determined depending on thecorrelation between the number of CCEs and a coding rate provided by theCCEs.

An eNB determines the PDCCH format according to DCI transmitted to a UEand adds a cyclic redundancy check (CRC) to the control information. TheCRC is masked by an identifier (ID) known as a radio network temporaryidentifier (RNTI) according to the owner or usage of the PDCCH. If thePDCCH is directed to a specific UE, its CRC may be masked by a cell-RNTI(C-RNTI) of the UE. If the PDCCH is for a paging message, the CRC of thePDCCH may be masked by a paging radio network temporary identifier(P-RNTI). If the PDCCH delivers system information, particularly, asystem information block (SIB), the CRC thereof may be masked by asystem information ID and a system information RNTI (SI-RNTI). Toindicate that the PDCCH delivers a random access response in response toa random access preamble transmitted by a UE, the CRC thereof may bemasked by a random access-RNTI (RA-RNTI).

FIG. 4 illustrates a UL subframe structure.

A UL subframe may be divided into a control region and a data region inthe frequency domain. A physical uplink control channel (PUCCH) carryinguplink control information is allocated to the control region and aphysical uplink shared channel (PUSCH) carrying user data is allocatedto the data region. To maintain a single carrier property, a UE does notsimultaneously transmit a PUSCH and a PUCCH. A PUCCH for a UE isallocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. This is called frequency hopping ofthe RB pair allocated to the PUCCH over a slot boundary.

Modeling of MIMO System

FIG. 5 illustrates configuration of a wireless communication systemhaving multiple antennas.

Referring to FIG. 5(a), if the number of transmit (Tx) antennasincreases to N_(T), and the number of receive (Rx) antennas increases toN_(R), a theoretical channel transmission capacity of the wirelesscommunication system increases in proportion to the number of antennas,differently from a case in which only a transmitter or receiver usesmultiple antennas, and accordingly transmission rate and frequencyefficiency may be significantly increased. In this case, the transferrate acquired by the increasing channel transmission capacity maytheoretically increased by a predetermined amount that corresponds tomultiplication of a maximum transfer rate (R_(o)) acquired when oneantenna is used by a rate of increase (R_(i)). The rate of increase(R_(i)) may be represented by the following Equation 1.

R _(i)=min(N _(T) ,N _(R))  Equation

For example, provided that a MIMO system uses four Tx antennas and fourRx antennas, the MIMO system may theoretically acquire a high transferrate which is four times that of a single antenna system. After theabove-mentioned theoretical capacity increase of the MIMO system wasdemonstrated in the mid-1990s, many developers began to conductintensive research into a variety of technologies which maysubstantially increase data transfer rate using the theoretical capacityincrease. Some of the above technologies have been reflected in avariety of wireless communication standards such as, for example,third-generation mobile communication and next-generation wireless LAN.

A variety of MIMO-associated technologies have been intensivelyresearched. For example, research into information theory associatedwith MIMO communication capacity under various channel environments ormultiple access environments, research into a radio frequency (RF)channel measurement and modeling of the MIMO system, and research intospace-time signal processing technology have been conducted.

Mathematical modeling of a communication method for use in theaforementioned MIMO system will hereinafter be described in detail. Itis assumed that the system includes N_(T) Tx antennas and N_(R) Rxantennas.

In the case of a transmission signal, the maximum number of pieces oftransmittable information is N_(T) under the condition that N_(T) Txantennas are used, and the transmission information may be representedby the following equation.

s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  Equation 2

Individual transmission pieces of information s₁, s₂, . . . , s_(NT) mayhave different transmit powers. In this case, if the individual transmitpowers are denoted by P₁, P₂, . . . , P_(NT), transmission informationhaving an adjusted transmit power may be represented by the followingequation.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ S ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  Equation 3

ŝ may be represented by the following equation using a diagonal matrix Pof transmit powers.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \mspace{11mu} & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

The information vector ŝ having adjusted transmit powers is applied to aweight matrix W, and thus N_(T) transmission signals x₁, x₂, . . . ,x_(NT) to be actually transmitted are configured. In this case, theweight matrix W serves to properly distribute transmission informationto individual antennas according to transmission channel situations. Theabove-mentioned transmission signals x₁, x₂, . . . , x_(NT) may berepresented by the following equation using vector X.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\; \hat{s}} = {WPs}}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Here, W_(ij) denotes a weight corresponding to the i-th Tx antenna andthe j-th information. W is also called a precoding matrix.

When N_(R) Rx antennas are used, received signals y₁, y₂, . . . , y_(NR)of individual antennas may be represented by a vector shown in thefollowing equation.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  Equation 6

When channel modeling is executed in the MIMO communication system,individual channels may be distinguished from each other according toTx/Rx antenna indexes. A specific channel from a Tx antenna j to an Rxantenna i is denoted by h_(ij). Regarding h_(ij), it should be notedthat an Rx antenna index is located ahead of a Tx antenna index.

FIG. 5(b) shows channels from N_(T) Tx antennas to Rx antenna i. Thechannels may be represented in the form of a vector or matrix. Referringto FIG. 5(b), the channels from the N_(T) Tx antennas to the Rx antennai may be represented by the following equation.

h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  Equation 7

All channels from the N_(T) Tx antennas to N_(R) Rx antennas may also berepresented as the following.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{T}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

Additive white Gaussian noise (AWGN) is added to an actual channel afterapplication of channel matrix H. AWGN n₁, n₂, . . . , n_(NR) added toeach of N_(R) Rx antennas may be represented by the following equation.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  Equation 9

Reception signal calculated by the mathematical modeling described abovemay be represented by the following equation.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

The number of rows and the number of columns of channel matrix Hindicating a channel condition are determined by the number of Tx/Rxantennas. In the channel matrix H, the number of rows is equal to thenumber (N_(R)) of Rx antennas, and the number of columns is equal to thenumber (N_(T)) of Tx antennas. Namely, the channel matrix H is denotedby an N_(R)×N_(T) matrix.

A rank of a matrix is defined by a smaller number between the number ofrows and the number of columns, in which the rows and the columns areindependent of each other. Therefore, the matrix rank may not be higherthan the number of rows or columns. The rank of the channel matrix H maybe represented by the following equation.

rank(H)≦min(N _(T) ,N _(R))  Equation 11

The rank may be defined as the number of non-zero Eigen values whenEigen value decomposition is performed on the matrix. Similarly, therank may be defined as the number of non-zero singular values whensingular value decomposition is performed on the matrix. Accordingly,the rank of the channel matrix refers to a maximum number of pieces ofinformation that may be transmitted on a given channel.

In this specification, “rank” with respect to MIMO transmissionindicates the number of paths through which signals may be independentlytransmitted at specific time in a specific frequency resource and “thenumber of layers” refers to the number of signal streams transmittedthrough each path. Since a transmitter transmits as many layers as therank used in signal transmission, the rank corresponds to the number oflayers unless otherwise mentioned.

Reference Signal (RS)

In transmitting packets in a wireless communication system, the packetsare transmitted over a radio channel, and therefore signal distortionmay occur in the transmission process. For a receive entity to receivethe correct signal in spite of signal distortion, the received distortedsignal should be corrected using channel information. In detecting thechannel information, a signal which is known to both the transmit entityand the receive entity is usually transmitted and the degree ofdistortion of the signal received over the channel is used to detect thechannel information. This signal is referred to as a pilot signal or areference signal.

When data is transmitted and received using multiple antennas, channelstate between each Tx antenna and each Rx antenna needs to be recognizedin order to receive a correct signal. Accordingly, a separate referencesignal needs to be present per Tx antenna.

The RSs may be broadly divided into two types according to the purposesthereof. One type is used to acquire channel information and the othertype is used for data demodulation. Since the former RS is used to allowthe UE to acquire DL channel information, this RS should be transmittedover a wide band, and even a UE which does not receive DL data in aspecific subframe should be receive and measure the RS. Such RS is alsoused for measurement of, for example, handover. The latter RS is sentwhen an eNB sends a resource on downlink. The UE may perform channelmeasurement by receiving this RS, thereby implementing data modulation.This RS should be transmitted in a region in which data is transmitted.

Legacy 3GPP LTE systems (e.g., 3GPP LTE Release-8) define two types ofdownlink RSs for the unicast service. One is a common RS (CRS), and theother is a dedicated RS (DRS). The CRS is used for acquisition ofinformation about the channel state and measurement of, for example,handover, and may be referred to as a cell-specific RS. The DRS is usedfor data demodulation, and may be referred to as a UE-specific RS. Inthe legacy 3GPP LTE systems, the DRS may be used only for datademodulation, and the CRS may be used for both acquisition of channelinformation and data demodulation.

The CRS is transmitted cell-specifically in every subframe in awideband. The CRS may be transmitted with respect to up to four antennaports depending on the number of Tx antennas of the eNB. For example, ifthe number of Tx antennas of the eNB is 2, CRSs for antenna ports #0 and#1 are transmitted. If the number of Tx antennas of the eNB is 4, CRSsfor antenna ports #0 to #3 are respectively transmitted.

FIG. 6 illustrates an exemplary pattern of a CRS and a DRS on one RBpair.

Referring to FIG. 6, the pattern of the CRS and the DRS is presented onone RB pair (14 OFDM symbols in the time domain×12 subcarriers in thefrequency domain in the case of normal CP) in a system in which the eNBsupports four transmit antennas. In FIG. 6, resource elements (REs)denoted by “R0”, “R1”, “R2” and “R3” represent the locations of the CRSsfor antenna port indexes 0, 1, 2 and 3, respectively. In FIG. 6, REsdenoted by “D” represent the locations of DRSs.

LTE-A, which is an advanced version of LTE, can supports up to 8 Txantennas on downlink. Accordingly, RSs for up to 8 Tx antennas need tobe supported in LTE-A. In LTE, downlink RSs are defined only for up to 4antenna ports. Therefore, if an eNB has 4 to 8 DL Tx antennas in LTE-A,RSs for these antenna ports need to be additionally defined. As the RSsfor up to 8 Tx antenna ports, both the RS for channel measurement andthe RS for data demodulation need to be considered.

One important consideration in designing an LTE-A system is backwardcompatibility. Backward compatibility refers to supporting the legacyLTE UE such that the legacy LTE UE normally operates in the LTE-Asystem. In terms of RS transmission, if RSs for up to 8 Tx antennas areadded to a time-frequency region in which a CRS defined in the LTEstandard is transmitted in every subframe over the full band, RSoverhead excessively increases. Accordingly, in designing new RSs for upto 8 antenna ports, reducing RS overhead needs to be considered.

The new RSs introduced in LTE-A may be classified into two types. One isa channel state information-RS (CSI-RS) intended for channel measurementfor selecting a transmission rank, a modulation and coding scheme (MCS),a precoding matrix index (PMI), and the like, and the other is ademodulation RS (DMRS) intended for demodulation of data transmittedthrough up to 8 Tx antennas.

The CSI-RS intended for channel measurement is designed only for channelmeasurement, unlike the existing CRS, which is used for datademodulation as well as for channel measurement and handovermeasurement. Of course, the CSI-RS may also be used for handovermeasurement. Since the CSI-RS is transmitted only in order to obtaininformation about channel states, the CSI-RS need not be transmitted inevery subframe, unlike the CRS for the legacy LTE system. Accordingly,to reduce overhead of the CSI-RS, the CSI-RS may be designed to beintermittently (e.g., periodically) transmitted in the time domain.

When data is transmitted in a certain DL subframe, a dedicated DMRS istransmitted to a UE for which the data transmission is scheduled. Thatis, the DMRS may be referred to as a UE-specific RS. A DMRS dedicated toa specific UE may be designed to be transmitted only in a resourceregion in which the UE is scheduled, i.e., the time-frequency region inwhich data for the UE is transmitted.

FIG. 7 illustrates an exemplary DMRS pattern defined in LTE-A.

FIG. 7 shows positions of REs for transmission of DMRSs on one RB pair(14 OFDM symbols in the time domain×12 subcarriers in the frequencydomain in the case of normal CP) on which downlink data is transmitted.The DMRS may be transmitted with respect to four antenna ports (antennaport indexes 7, 8, 9 and 10) which are additionally defined in LTE-A.DMRSs for different antenna ports may be distinguished from each otheras they are positioned on different frequency resources (subcarriers)and/or different time resources (OFDM symbols) (namely, they may bemultiplexed using FDM and/or TDM). DMRSs for different antenna portspositioned on the same time-frequency resource may be distinguished fromeach other by an orthogonal code (namely, they may be multiplexed usingthe CDM scheme). In the example of FIG. 7, DMRSs for antenna ports 7 and8 may be positioned on the REs indicated by DMRS CDM Group 1 and bemultiplexed by an orthogonal code. Similarly, in the example of FIG. 7,DMRSs for antenna ports 9 and 10 may be positioned on the REs indicatedby DMRS Group 2 and be multiplexed by the orthogonal code.

When the eNB transmits a DMRS, the precoding applied to data is appliedto the DMRS. Accordingly, the channel information estimated by the UEusing the DMRS (or UE-specific RS) is precoded channel information. TheUE may easily perform data demodulation using the precoded channelinformation estimated through the DMRS. However, the UE does not knowthe information about the precoding applied to the DMRS, and accordinglythe UE may not acquire, from the DMRS, channel information that is notprecoded. The UE may acquire the channel information that is notprecoded, using an RS separate from the DMRS, namely using the CSI-RSmentioned above.

FIG. 8 is a diagram illustrating exemplary CSI-RS patterns defined inLTE-A.

FIG. 8 shows positions of REs for transmission of CSI-RSs on one RB pair(14 OFDM symbols in the time domain×12 subcarriers in the frequencydomain in the case of normal CP) on which downlink data is transmitted.One of CSI-RS patterns shown in FIGS. 8(a) to 8(e) may be used in a DLsubframe. CSI-RSs may be transmitted with respect to 8 antenna ports(antenna port indexes 15, 16, 17, 18, 19, 20, 21 and 22) which areadditionally defined in LTE-A. CSI-RSs for different antenna ports maybe distinguished from each other as they are positioned on differentfrequency resources (subcarriers) and/or different time resources (OFDMsymbols) (namely, they may be multiplexed using FDM and/or TDM). CSI-RSsfor different antenna ports positioned on the same time-frequencyresource may be distinguished from each other by an orthogonal code(namely, they may be multiplexed using CDM). In the example of FIG.8(a), CSI-RSs for antenna ports 15 and 16 may be positioned on the REsindicated by CSI-RS CDM Group 1 and be multiplexed by an orthogonalcode. In the example of FIG. 8(a), CSI-RSs for antenna ports 17 and 18may be positioned on the REs indicated by CSI-RS CDM Group 2 and bemultiplexed by the orthogonal code. CSI-RSs for antenna ports 19 and 20may be positioned on the REs indicated by CSI-RS CDM Group 3 and bemultiplexed by the orthogonal code. In the example of FIG. 8(a), CSI-RSsfor antenna ports 21 and 22 may be positioned on the REs indicated byCSI-RS CDM Group 4 and multiplexed by the orthogonal code. The principledescribed above with reference to FIG. 8(a) may also be applied to FIGS.8(b) to 8(e).

The RS patterns of FIGS. 6 to 8 are simply illustrative, and embodimentsof the present invention are not limited to specific RS patterns. Inother words, the embodiments of the present invention may be applied inthe same manner when an RS pattern different from those of FIGS. 6 to 8is defined and used.

CSI-RS Configuration

As described above, in the LTE-A system supporting up to 8 Tx antennason downlink, an eNB needs to transmit CSI-RSs for all antenna ports.Since transmitting CSI-RSs for a maximum of 8 Tx antenna ports in everysubframe excessively increases overhead, the CSI-RS may need to beintermittently transmitted in the time domain to reduce overhead, ratherthan being transmitted in every subframe. Accordingly, the CSI-RS may beperiodically transmitted with a periodicity corresponding to an integermultiple of one subframe or transmitted in a specific transmissionpattern.

Here, the periodicity or pattern in which the CSI-RS is transmitted maybe configured by a network (e.g., an eNB). To perform CSI-RS-basedmeasurement, the UE should be aware of a CSI-RS configuration for eachCSI-RS antenna port of a cell (or a TP) to which the UE belongs. TheCSI-RS configuration may include the index of a downlink subframe inwhich a CSI-RS is transmitted, time-frequency positions (e.g., a CSI-RSpattern as shown in FIGS. 8(a) to 8(e)) of CSI-RS REs in a transmissionsubframe, and a CSI-RS sequence (which is a sequence intended for CSI-RSand pseudo-randomly generated based on the slot number, cell ID, CPlength and the like according to a predetermined rule). That is, a giveneNB may use a plurality of CSI-RS configurations, and inform of CSI-RSconfigurations to be used for UE(s) in a cell among the CSI-RSconfigurations.

The plurality of CSI-RS configurations may or may not include a CSI-RSconfiguration for which the UE assumes that the transmit power of theCSI-RS is non-zero power. In addition, the plurality of CSI-RSconfigurations may or may not include at least one CSI-RS configurationfor which the UE assumes that the transmit power of the CSI-RS is zerotransmit power.

Further, each bit of a parameter (e.g., a 16-bit bitmap ZeroPowerCSI-RSparameter) for a CSI-RS configuration of zero transmit power may becaused by a higher layer to correspond to the CSI-RS configuration (orREs to which CSI-RSs can be allocated according to the CSI-RSconfiguration), and the UE may assume that the transmit power on theCSI-RS REs of a CSI-RS configuration corresponding to a bit set to 1 inthe parameter is 0.

Since CSI-RSs for the respective antenna ports need to be distinguishedfrom each other, resources on which the CSI-RSs for the antenna portsare transmitted need to be orthogonal to each other. As described abovein relation to FIG. 8, the CSI-RSs for the antenna ports may bemultiplexed using FDM, TDM and/or CDM using orthogonal frequencyresources, orthogonal time resources and/or orthogonal code resources.

When the eNB informs a UE belonging to a cell thereof of informationabout CSI-RSs, the eNB needs to signal information about time andfrequency to which a CSI-RS for each antenna port is mapped.Specifically, the information about time may include the subframenumbers of subframes in which the CSI-RS is transmitted, a CSI-RStransmission periodicity for transmission of the CSI-RS, a subframeoffset for transmission of the CSI-RS, and a number corresponding to anOFDM symbol on which a CSI-RS RE of a specific antenna is transmitted.The information about frequency may include spacing of frequencies atwhich a CSI-RS RE of a specific antenna is transmitted, and an RE offsetor a shift value in the frequency domain.

FIG. 9 is a diagram illustrating an exemplary scheme in which a CSI-RSis periodically transmitted.

The CSI-RS may be periodically transmitted with a periodicitycorresponding to an integer multiple of one subframe (e.g., 5 subframes,10 subframes, 20 subframes, 40 subframes, or 80 subframes)

FIG. 9 illustrates a case in which one radio frame consists of 10subframes (from subframe 0 to subframe 9). In the example illustrated inFIG. 9, the transmission periodicity of the CSI-RS of the eNB is 10 ms(i.e., 10 subframes), and the CSI-RS transmission offset is 3. Differentoffset values may be assigned to eNBs such that CSI-RSs of several cellsare uniformly distributed in the time domain. When the CSI-RS istransmitted with a periodicity of 10 ms, the offset may be set to avalue between 0 and 9. Similarly, when the CSI-RS is transmitted with aperiodicity of, for example, 5 ms, the offset may be set to a valuebetween 0 and 4. When the CSI-RS is transmitted with a periodicity of 20ms, the offset may be set to a value between 0 and 19. When the CSI-RSis transmitted with a periodicity of 40 ms, the offset may be set to avalue between 0 and 39. When the CSI-RS is transmitted with aperiodicity of 80 ms, the offset may be set to a value between 0 and 79.The offset value indicates the value of a subframe in which an eNBtransmitting the CSI-RS with a predetermined periodicity starts CSI-RStransmission. When the eNB informs the UE of the transmissionperiodicity and the offset value of the CSI-RS, the UE may receive theCSI-RS of the eNB at the corresponding subframe position, using thevalues. The UE may measure a channel through the received CSI-RS, andreport information such as CQI, PMI and/or rank indicator (RI) to theeNB as a result of the measurement. The CQI, the PMI and the RI may becollectively referred to as CQI (or CSI) throughout the specificationunless they are separately described. The aforementioned informationrelated to the CSI-RS is cell-specific information and may be applied tothe UEs in a cell in common. The CSI-RS transmission periodicity andoffset may be separately specified for each CSI-RS configuration. Forexample, a separate CSI-RS transmission periodicity and offset may beset for a CSI-RS configuration representing a CSI-RS transmitted withzero transmit power and a CSI-RS configuration representing a CSI-RStransmitted with non-zero transmit power.

Contrary to the CRS transmitted in all subframes in which a PDSCH can betransmitted, the CSI-RS may be configured to be transmitted only in somesubframes. For example, CSI subframe sets C_(CSI,0) and C_(CSI,1) may beconfigured by a higher layer. CSI reference resource (i.e., apredetermined resource region forming the basis of CSI calculation) maybelong to either C_(CSI,0) or C_(CSI,1), may not belong to bothC_(CSI,0) and C_(CSI,1) at the same time. Accordingly, when CSI subframesets C_(CSI,0) and C_(CSI,1) are configured by a higher layer, the UE isnot allowed to expect that it will receive a trigger (or an indicationfor CSI calculation) for a CSI reference resource which is present in asubframe which belongs to none of the CSI subframe sets.

Alternatively, the CSI reference resource may be configured in a validdownlink subframe. The valid downlink subframe may be configured as asubframe satisfying various conditions. In the case of periodic CSIreporting, one of the conditions may be a subframe belonging to a CSIsubframe set that is linked to periodic CSI reporting when a CSIsubframe set is configured for the UE.

The UE may derive a CQI index from the CSI reference resource inconsideration of the following assumptions (For details, see 3GPP TS36.213).

-   -   First three OFDM symbols in a subframe are occupied by control        signaling.    -   No REs are used by a primary synchronization signal, a secondary        synchronization signal, or a physical broadcast channel (PBCH).    -   CP length of a non-Multicast Broadcast Single Frequency Network        (MBSFN) subframe.    -   Redundancy version is 0.    -   If a CSI-RS is used for channel measurement, the ratio of PDSCH        energy per resource element (EPRE) to CSI-RS EPRE conforms to a        predetermined rule.    -   For CST reporting in transmission mode 9 (i.e., the mode        supporting up to S-layer transmission), if the UE is configured        for PMI/RI reporting, it is assumed that DMRS overhead        corresponds to the most recently reported rank. For example, in        the case of two or more antenna ports (i.e., rank less than or        equal to 2) as described in FIG. 7, DMRS overhead on one RB pair        is 12 REs, whereas DMRS overhead in the case of three or more        antenna ports (i.e., rank greater than or equal to 3) is 24 REs.        Therefore, a CQI index may be calculated on the assumption of        DMRS overhead corresponding to the most recently reported rank        value.    -   No REs are allocated to a CSI-RS and a zero-power CSI-RS.    -   No REs are allocated to a positioning RS (PRS).    -   The PDSCH transmission scheme conforms to a transmission mode        currently set for the UE (the mode may be a default mode).    -   The ratio of PDSCH EPRE to cell-specific RS EPRE conforms to a        predetermined rule.

The eNB may inform UEs of such a CSI-RS configuration through, forexample, radio resource control (RRC) signaling. That is, informationabout the CSI-RS configuration may be provided to UEs in a cell usingdedicated RRC signaling. For example, while a UE establishes aconnection with the eNB through initial access or handover, the eNB mayinform the UE of the CSI-RS configuration through RRC signaling.Alternatively, when the eNB transmits, to a UE, an RRC signaling messagedemanding channel state feedback based on CSI-RS measurement, the eNBmay inform the UE of the CSI-RS configuration through the RRC signalingmessage.

Meanwhile, locations of the CSI-RS in the time domain, i.e. acell-specific subframe configuration period and a cell-specific subframeoffset, may be summarized as shown in Table 1 below.

TABLE 1 CSI-RS subframe CSI-RS periodicity CSI-RS subframe offsetconfiguration T_(CSI-RS) Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes)0-4 5 I_(CSI-RS)  5-14 10 I_(CSI-RS)-5 15-34 20 I_(CSI-RS)-15 35-74 40I_(CSI-RS)-35  75-154 80 I_(CSI-RS)-75

As described above, parameter I_(CSI-RS) may be separately configuredfor a CSI-RS assumed to have a non-zero transmit power by the UE and aCSI-RS assumed to have zero transmit power by the UE. A subframeincluding a CSI-RS may be represented by Equation 12 below (In Equation12, n_(f) is a system frame number and n_(s) is a slot number).

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  Equation 12

CSI-RS-Config information elements (IEs) defined as in Table 2 below maybe used to specify a CSI-RS configuration.

TABLE 2 CSI-RS-Config information elements -- ASN1STARTCSI-RS-Config-r10 ::= SEQUENCE { csi-RS-r10 CHOICE { release NULL, setupSEQUENCE { antennaPortsCount-r10 ENUMERATED {an1, an2, an4, an8},resourceConfig-r10 INTEGER (0..31), subframeConfig-r10 INTEGER (0..154),p-C-r10 INTEGER (−8..15) } } OPTIONAL, -- Need ON zeroTxPowerCSI-RS-r10CHOICE { release NULL, setup SEQUENCE {zeroTxPowerResourceConfigList-r10 BIT STRING (SIZE (16)),zeroTxPowerSubframeConfig-r10 INTEGER (0..154) } } OPTIONAL  -- Need ON} -- ASN1STOP

In Table 2, parameter ‘antennaPortsCount’ indicates the number ofantenna ports (i.e., CSI-RS ports). In this parameter, an1 correspondsto one antenna port, and an2 corresponds to two antenna ports.

In Table 2, parameter ‘p_C’ indicates a ratio between PDSCH energy perresource element (EPRE) and CSI-RS EPRE that is assumed when the UEderives CSI feedback.

In Table 2, parameter ‘resourceConfig’ has, for example, a value thatdetermines the position of an RE to which a CSI-RS is mapped on an RBpair, as shown in FIG. 8.

In Table 2, parameter ‘subframeConfig’ corresponds to T_(CSI-RS) inTable 1.

In Table 2, zeroTxPowerResourceConfigList and zeroTxPowerSubframeConfigcorrespond to resourceConfig and subframeConfig of a CSI-RS having azero transmit power, respectively.

For details of the CSI-RS configuration IE of Table 2, see standarddocument TS 36.331.

Generation of CSI-RS Sequence

The RS sequence r_(l,n) _(s) ^((m)) may be defined as Equation 13 below.

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots \;,{N_{RB}^{\max,{DL}} - 1}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

In Equation 13, n_(s) denotes a slot number (or a slot index) in asubframe, and l denotes an OFDM symbol number (or OFDM symbol index) ina slot. c(i), which denotes a pseudo-random sequence, is defined as alength-31 gold sequence. In generating a pseudo-random sequence, aninitialization value is given as c_(init). c_(init) may be given asEquation 14 below.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)  Equation 14

In Equation 13, n_(s) denotes a slot number (or a slot index) in asubframe, and l denotes an OFDM symbol number (or OFDM symbol index) ina slot. N_(ID) ^(cell) denotes a physical layer cell identifier. N_(CP)is set to 1 for normal CP and to 0 for extended CP.

For details of generation of a CSI-RS sequence, see standard document TS36.211 v10.4.0.

Channel Status Information (CSI)

MIMO schemes may be classified into open-loop MIMO and closed-loop MIMO.In open-loop MIMO, a MIMO transmitter performs MIMO transmission withoutreceiving CSI feedback from a MIMO receiver. In closed-loop MIMO, theMIMO transmitter receives CSI feedback from the MIMO receiver and thenperforms MIMO transmission. In closed-loop MIMO, each of the transmitterand the receiver may perform beamforming based on the CSI to achieve amultiplexing gain of MIMO Tx antennas. To allow the receiver (e.g., aUE) to feed back CSI, the transmitter (e.g., an eNB) may allocate a ULcontrol channel or a UL-SCH to the receiver.

The UE may perform estimation and/or measurement of a downlink channelusing a CRS and/or a CSI-RS. The CSI fed back to the eNB by the UE mayinclude a rank indicator (RI), a precoding matrix indicator (PMI), and achannel quality indicator (CQI).

The RI is information about a channel rank. The channel rank representsthe maximum number of layers (or streams) that can carry differentpieces of information in the same time-frequency resources. Since therank is determined mainly according to long-term fading of a channel,the RI may be fed back with a longer periodicity (namely, lessfrequently) than the PMI and the CQI.

The PMI is information about a precoding matrix used for transmissionfrom a transmitter and has a value reflecting the spatialcharacteristics of a channel. Precoding refers to mapping transmissionlayers to Tx antennas. A layer-antenna mapping relationship may bedetermined by the precoding matrix. The PMI corresponds to an index of aprecoding matrix of an eNB preferred by the UE based on a metric such assignal-to-interference-plus-noise ratio (SINR). In order to reduce thefeedback overhead of precoding information, the transmitter and thereceiver may pre-share a codebook including multiple precoding matrices,and only the index indicating a specific precoding matrix in thecodebook may be fed back. For example, the PMI may be determined basedon the most recently reported RI.

The CQI is information indicating channel quality or channel strength.The CQI may be expressed as a predetermined MCS combination. That is, aCQI index that is fed back indicates a corresponding modulation schemeand code rate. The CQI may configure a specific resource region (e.g., aregion specified by a valid subframe and/or a physical RB) as a CQIreference resource and be calculated on the assumption that PDSCHtransmission is present on the CQI reference resource, and the PDSCH canbe received without exceeding a predetermined error probability (e.g.,0.1). Generally, the CQI has a value reflecting a received SINR whichcan be obtained when the eNB configures a spatial channel using a PMI.For instance, the CQI may be calculated based on the most recentlyreported RI and/or PMI.

In a system supporting an extended antenna configuration (e.g., an LTE-Asystem), additional acquisition of multi user (MU)-MIMO diversity usingan MU-MIMO scheme is considered. In the MU-MIMO scheme, when an eNBperforms downlink transmission using CSI fed back by one UE amongmultiple users, it is necessary to prevent interference with other UEsbecause there is an interference channel between UEs multiplexed in theantenna domain. Accordingly, CSI of higher accuracy than in asingle-user (SU)-MIMO scheme should be fed back in order to correctlyperform MU-MIMO operation.

A new CSI feedback scheme may be adopted by modifying the existing CSIincluding an RI, a PMI, and a CQI so as to measure and report moreaccurate CSI. For example, precoding information fed back by thereceiver may be indicated by a combination of two PMIs (e.g., i1 andi2). Thereby, more precise PMI may be fed back, and more precise CQI maybe calculated and reported based on such precise PMI.

Meanwhile, the CSI may be periodically transmitted over a PUCCH and oraperiodically transmitted over a PUSCH. For the RI, various reportingmodes may be defined depending on which of a first PMI (e.g., W1), asecond PMI (e.g., W2), and a CQI is fed back and whether the PMI and/orCQI that is fed back relates to a wideband (WB) or a subband (SB).

CQI Calculation

Hereinafter, CQI calculation will be described in detail on theassumption that the downlink receiver is a UE. However, the descriptionof the present invention given below may also be applied to a relaystation serving to perform downlink reception.

A description will be given below of a method for configuring/defining aresource (hereinafter, referred to as a reference resource) forming thebasis of calculation of the CQI when the UE reports CSI. The CQI is morespecifically defined below.

A CQI that the UE reports corresponds to a specific index value. The CQIindex has a value indicating a modulation technique, code rate, and thelike that correspond to the channel state. For example, CQI indexes andanaylized meanings thereof may be given as shown in Table 3 below.

TABLE 3 CQI index Modulation Code rate × 1024 Efficiency 0 out of range1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK 193 0.3770 4 QPSK 308 0.6016 5QPSK 449 0.8770 6 QPSK 602 1.1758 7 16QAM 378 1.4766 8 16QAM 490 1.91419 16QAM 616 2.4063 10 64QAM 466 2.7305 11 64QAM 567 3.3223 1 64QAM 6663.9023 13 64QAM 772 4.5234 14 64QAM 873 5.1152 15 64QAM 948 5.5547

Based on an observation which is not restricted by time and frequency,the UE may determine the highest CQI index satisfying a predeterminedrequirement among CQI indexes 1 to 15 of Table 3 with respect to eachCQI value reported in uplink subframe n. The predetermined requirementmay be that a single PDSCH transmission block which has a combination ofa modulation scheme (e.g., MCS) and a transmission block size (TBS)corresponding to the CQI index and occupies a group of downlink physicalRBs called a CQI reference resource should be received with atransmission block error probability not exceeding 0.1 (i.e., 10%). Ifeven CQI index 1 does not satisfy the aforementioned requirement, the UEmay determine CQI index 0.

In transmission mode 9 (corresponding to transmission of up to 8 layers)and the feedback reporting mode, the UE may perform channel measurementfor calculation of the CQI value reported in uplink subframe n basedonly on the CSI-RS. In the other transmission modes and correspondingreporting modes, the UE may perform channel measurement for CQIcalculation based on the CRS.

If all requirements given below are satisfied, a combination of amodulation scheme and a TBS may correspond to one CQI index. That is,the combination should be allowed to be signaled on a PDSCH in a CQIreference resource according to an associated TRS table, the modulationscheme should be indicated by a corresponding CQI index, and when thecombination of a TBS and a modulation scheme is applied to the referenceresource, a valid channel code rate as close to the code rate indicatedby the CQI index as possible should be given. If two or morecombinations of a TBS and a modulation scheme are almost equal to thecode rate indicated by the corresponding CQI index, a combination havingthe smallest TBS may be determined.

A CQI reference resource is defined as the following.

In the frequency domain, the CQI reference resource defined as a groupof downlink physical RBs corresponds to a band associated with thederived CQI value.

In the time domain, the CQI reference resource is defined as a singledownlink subframe n-nCQI_ref. In the case of periodic CQI reporting,nCQI_ref is determined to have a value that is smallest among the valuesgreater than or equal to 4 and corresponds to a downlink subframe inwhich downlink subframe n-nCQI_ref is valid. In the case of aperiodicCQI reporting, a downlink subframe identical to a valid downlinksubframe corresponding to a CQI request in an uplink DCI format (namely,the PDCCH DCI format for providing the UE with uplink scheduling controlinformation) (or having a received CQI request) is determined as a CQIreference resource for nCQI_ref. In aperiodic CQI reporting, nCQI_refmay be 4, and downlink subframe n-nCQI_ref may correspond to a validdownlink subframe. Herein, downlink subframe n-nCQI_ref may be receivedafter a subframe corresponding to a CQI request in a random accessresponse grant (or having a received CQI request). The valid downlinksubframe refers to a downlink subframe that is configured for the UE, isnot set as a MBSFN subframe except in transmission mode 9, and neitherincludes a DwPTS field if the length of DwPTS is less than or equal to7680*Ts (Ts=1/(15000×2048) seconds), nor belongs to a measurement gapconfigured for the UE. If there is no valid downlink subframe for theCQI reference resource, CQI reporting is not performed in uplinksubframe n.

In the layer region, the CQI reference resource is defined as a RI andPMI which the CQI presumes.

The following assumptions may be made for the UE to derive a CQI indexon a CQI reference resource: (1) the first three OFDM symbols in adownlink subframe are used for control signaling; (2) there is no REthat is used by a primary synchronization signal, a secondarysynchronization signal, or a PBCH; (3) CP length of a non-MBSFN subframeis given; (4) Redundancy version is 0; (5) If a CSI-RS is used forchannel measurement, the ratio of PDSCH energy per resource element(EPRE) to CSI-RS EPRE has a predetermined value signaled by a higherlayer; (6) a PDSCH transmission scheme (single antenna porttransmission, transmission diversity, spatial multiplexing, MU-MIMO,etc.) defined for each transmission mode (e.g., a default mode) iscurrently set for the UE; (7) if the CRS is used for channelmeasurement, the ratio of PDSCH EPRE to CRS EPRE may be determinedaccording to a predetermined requirement. For details related todefinition of the CQI, see 3GPP TS 36.213.

In summary, the downlink receiver (e.g., a UE) may configure a specificsingle subframe of the past as a CQI reference resource with respect tothe current time at which it is performing CQI calculation, and when aPDSCH is transmitted from the eNB on the CQI reference resource, maycalculate a CQI value such that a condition that the error probabilityshould not exceed 10% is satisfied.

Coordinated Multi-Point (CoMP)

To satisfy enhanced system performance requirements for the 3GPP LTE-Asystem, CoMP transmission and reception technology (also called co-MIMO,collaborative MIMO or network MIMO) has been proposed. CoMP technologymay increase performance of UEs located at a cell edge and averagesector throughput.

In a multi-cell environment with a frequency reuse factor set to 1, theperformance of a UE located at a cell edge and average sector throughputmay be lowered due to inter-cell interference (ICI). To attenuate ICI,the legacy LTE system has adopted a simple passive technique such asfractional frequency reuse (FFR) based on UE-specific power control suchthat a UE located at a cell edge may have appropriate throughputperformance in an environment constrained by interference. However,attenuating the ICI or reusing ICI as a desired signal for the UE may bemore desirable than using fewer frequency resources per cell. To thisend, a CoMP transmission technique may be employed.

CoMP schemes applicable to downlink may be broadly classified into jointprocessing (JP) and coordinated scheduling/beamforming (CS/CB).

According to the JP scheme, data can be used by each transmission point(eNB) of a CoMP cooperation unit. The CoMP cooperation unit refers to aset of eNBs used for a CoMP transmission scheme. The JP scheme may befurther divided into joint transmission and dynamic cell selection.

Joint transmission refers to a technique of simultaneously transmittingPDSCHs from a plurality of points (a part or the entirety of a CoMPcooperation unit). That is, a plurality of transmission points maysimultaneously transmit data to a single UE. With the joint transmissionscheme, the quality of a received signal may be coherently ornon-coherently improved, and interference with other UEs may be activelyeliminated.

Dynamic cell selection is a technique of transmitting a PDSCH from onepoint (of a CoMP cooperation unit) at a time. That is, one pointtransmits data to a single UE at a given time point, while the otherpoints in the CoMP cooperation unit do not transmit data to the UE atthe time point. A point to transmit data to a UE may be dynamicallyselected.

Meanwhile, in the CS/CB scheme, CoMP cooperation units may cooperativelyperform beamforming for data transmission to a single UE. While data istransmitted to the UE only from a serving cell, userscheduling/beamforming may be determined through coordination amongcells of the CoMP cooperation units.

In the case of uplink, CoMP reception refers to reception of a signaltransmitted through cooperation among a plurality of geographicallyseparated points. CoMP schemes applicable to uplink may be classifiedinto joint reception (JR) and coordinated scheduling/beamforming(CS/CB).

The JR scheme indicates that a plurality of reception points receives asignal transmitted through a PUSCH. The CS/CB scheme indicates that onlyone point receives a PUSCH, and user scheduling/beamforming isdetermined by coordination among the cells of the CoMP unit.

With a CoMP system as above, multi-cell base stations may jointlysupport data for a UE. In addition, the base stations may simultaneouslysupport one or more UEs using the same radio frequency resources,thereby increasing system performance. Moreover, a base station mayperform space division multiple access (SDMA) based on CSI between theUE and the base station.

In the CoMP system, a serving eNB and one or more cooperative eNBs areconnected to a scheduler over a backbone network. The scheduler mayreceive channel information about the channel states between each UE andcooperative eNBs measured and fed back by the cooperative eNBs over thebackbone network, and operate based on the channel information. Forexample, the scheduler may schedule information for a cooperative MIMOoperation for the serving eNB and the one or more cooperative eNBs. Thatis, the scheduler may directly give each eNB a command to perform thecooperative MIMO operation.

As noted from the above description, it can be said that the CoMP systemoperates as a virtual MIMO system by grouping a plurality of cells intoone group. Basically, the CoMP system may adopt a MIMO communicationscheme employing multiple antennas.

Carrier Aggregation

Before description is given of carrier aggregation, the concept of cellintroduced to manage radio resources in LTE-A will be described first. Acell may be understood as a combination of downlink resources and uplinkresources. Here, the uplink resource is not an essential element of thecell. Accordingly, a cell may include only downlink resources or includedownlink resources and uplink resources. The downlink resource may bereferred to as a downlink component carrier (DL CC), and the uplinkresource may be referred to as an uplink component carrier (UL CC). TheDL CC and the UL CC may be represented by carrier frequencies, and acarrier frequency represents a center frequency within the correspondingcell.

Cells may be divided into a primary cell (PCell), which operates at aprimary frequency, and a secondary cell (SCell), which operates at asecondary frequency. The PCell and the SCell may be collectivelyreferred to as a serving cell. A cell designated when the UE performs aninitial connection establishment procedure or during a connectionre-establishment procedure or a handover procedure, may serve as thePCell. In other words, the PCell may be understood as a cell that servesas a control-related center in a carrier aggregation environment, whichwill be described in detail later. A UE may be assigned a PUCCH in thePCell thereof and may then transmit the assigned PUCCH. The SCell may beconfigured after establishment of radio resource control (RRC)connection, and SCell may be used for providing additional radioresources. In the carrier aggregation environment, all serving cellsexcept the PCell may be viewed as SCells. In the case in which a UE isin an RRC_CONNECTED state but carrier aggregation is not established orin a case in which the UE does not support carrier aggregation, only asingle serving cell consisting of PCells exists. On the other hand, inthe case in which a UE is in the RRC_CONNECTED state and carrieraggregation is established therefor, one or more serving cells exist,and PCells and all SCells are included in all serving cells. For a UEsupporting carrier aggregation, after an initial security activationprocedure is initiated, the network may configure one or more SCells inaddition to a PCell configured at the beginning of the connectionestablishment procedure.

FIG. 10 Illustrates Carrier Aggregation

Carrier aggregation is a technology that has been introduced to allowfor use of a broader band in order to meet the requirements of ahigh-speed transmission rate. Carrier aggregation may be defined as anaggregation of two or more component carriers (CCs) having differentcarrier frequencies or an aggregation of two or more cells. Referring toFIG. 10, FIG. 10(a) illustrates a subframe in a case when one CC is usedin the legacy LTE system, and FIG. 10(b) illustrates a subframe in acase where carrier aggregation is used. For example, in FIG. 10(b), 3CCs of 20 MHz are used, thereby supporting a bandwidth of 60 MHz.Herein, CCs may be continuous or non-continuous in the frequency domain.

The UE may simultaneously receive and monitor downlink data from aplurality of DL CCs. A linkage between a DL CC and a UL CC may beindicated by the system information. The DL CC/UL CC link may be fixedin the system or may be semi-statically configured. Additionally, evenif the entire system band consists of N CCs, the frequency band in whicha specific UE can perform monitoring/reception may be limited to M(<N)CCs. Various parameters for carrier aggregation may be set up in acell-specific, UE group-specific, or UE-specific manner.

FIG. 11 Illustrates Cross-Carrier Scheduling.

Cross-carrier scheduling refers to, for example, including all downlinkscheduling allocation information about a DL CC in the control region ofanother DL CC for one of multiple serving cells or including all uplinkscheduling grant information about multiple UL CCs linked to a DL CC forone of multiple serving cells in the control region of the DL CC.

Regarding cross-carrier scheduling, a carrier indicator field (CIF) willbe described first. The CIF may be included in the DCI formattransmitted over the PDCCH (and be defined to have, for example, thesize of 3 bits), or may not be included in the DCI format (in this case,the CIF may be defined to have, for example, the size of 0 bit). If theCIF is included in the DCI format, this indicates that cross-carrierscheduling is applied. In the case in which cross-carrier scheduling isnot applied, the downlink scheduling allocation information is validwithin the DL CC through which downlink scheduling allocationinformation is currently being transmitted. Additionally, the uplinkscheduling grant is valid for a UL CC linked to the DL CC through whichthe downlink scheduling allocation information is transmitted.

In the case in which cross-carrier scheduling is applied, the CIFindicates a CC related to the downlink scheduling allocation informationwhich is transmitted over the PDCCH in a DL CC. For example, referringto FIG. 11, downlink allocation information about DL CC B and DL CC C,i.e., information about PDSCH resources, is transmitted over the PDCCHwithin the control region of DL CC A. The UE may monitor DL CC A so asto recognize the resource region of the PDSCH and the corresponding CCthrough the CIF.

Whether or not the CIF is included in the PDCCH may be semi-staticallyset, and the CIF may be UE-specifically enabled by higher-layersignaling.

When the CIF is disabled, the PDCCH in a specific DL CC allocates aPDSCH resource in the same DL CC and may also allocate a PUSCH resourcein a UL CC linked to the specific DL CC. In this case, the same codingscheme, CCE-based resource mapping, DCI format, and so on, as in thelegacy PDCCH structure, may be applied.

When the CIF is enabled, the PDCCH in a specific DL CC may allocate aPDSCH/PUSCH resource within a single DL/UL CC indicated by the CIF,among the multiple aggregated CCs. In this case, a CIF may beadditionally defined in the legacy PDCCH DCI format. The CIF may bedefined as a field having a fixed length of 3 bits, or the CIF positionmay be fixed regardless of the size of the DCI format. The codingscheme, CCE-based resource mapping, DCI format, and so on of the legacyPDCCH structure may be applied to this case.

When the CIF exists, an eNB may allocate a DL CC set in which the PDCCHis to be monitored. Accordingly, the burden of blind decoding to the UEmay be lessened. The PDCCH monitoring CC set corresponds to a portion ofall aggregated DL CCs, and the UE may perform PDCCH detection/decodingonly in the corresponding CC set. In other words, in order to performPDSCH/PUSCH scheduling for a UE, the eNB may transmit the PDCCH only inthe PDCCH monitoring CC set. The PDCCH monitoring CC set may beUE-specifically or UE group-specifically or cell-specificallyconfigured. For example, when 3 DL CCs are aggregated as illustrated inFIG. 6, DL CC A may be configured as a PDCCH monitoring DL CC. If theCIF is disabled, the PDCCH in each DL CC may schedule only the PDSCHwithin the DL CC A. On the other hand, if the CIF is enabled, the PDCCHin DL CC A may schedule not only the PDCCH of the DL CC A but also thePDSCH of the other DL CCs. In the case where the DL CC A is configuredas the PDCCH monitoring CC, the PDCCH may not be transmitted in DL CC Band DL CC C.

PDCCH Processing

Control channel elements (CCEs), which are contiguous logical allocationunits, are used in mapping PDCCHs to REs. A CCE includes a plurality ofresource element groups (e.g., 9 REGs). Each REG includes four REs whichmay neighbor each other if the RS is excluded.

The number of CCEs necessary for a specific PDCCH depends on a DCIpayload corresponding to the size of control information, a cellbandwidth, a channel coding rate, etc. Specifically, the number of CCEsfor a specific PDCCH may be defined according to PDCCH formats as shownin Table 4.

TABLE 4 Number of Number of PDCCH PDCCH format Number of CCEs REGs bits0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

One of the four formats may be used for a PDCCH, but this is not knownto the UE. Accordingly, the UE needs to perform decoding without knowingthe PDCCH format. This is called blind decoding. Since decoding as manyCCEs used for downlink as possible for each PDCCH format causessignificant load to the UE, a search space is defined in considerationof restriction on the scheduler and the number of attempts to performdecoding.

That is, the search space is an aggregation of candidate PDCCHsincluding CCEs which the UE needs to attempt to decode at an aggregationlevel. Each aggregation level and the corresponding number of candidatePDCCHs may be defined as shown in Table 5 below.

TABLE 5 Search space Size Number of PDCCH Aggregation level (in CCEunits) candidates UE-specific 1 6 6 2 12 6 4 8 2 8 16 2 Common 4 16 4 816 2

As shown in Table 5, there are 4 aggregation levels, and the UE has aplurality of search spaces according to the aggregation levels. Thesearch spaces may be divided into a UE-specific search space and acommon search space, as shown in Table 5. The UE-specific search spaceis for specific UEs. Each UE may check an RNTI and CRC with which thePDCCH is masked, by monitoring the UE-specific search space thereof(attempting to decode an aggregation of PDCCH candidates according to apossible DCI format) and acquire control information if the RNTI and CRCare valid.

The common search space is intended for use in the case in which aplurality of UEs or all UEs need to receive PDCCHs, as in the cases ofsystem information dynamic scheduling and paging messages. The commonsearch space may be used for a specific UE in terms of resourcemanagement. Furthermore, the common search space may overlap theUE-specific search space.

In this manner, the UE attempts to perform decoding in a search space.The number of decoding attempts is determined by a DCI format and atransmission mode determined through radio resource control (RRC)signaling. If carrier aggregation is not applied, the UE needs toattempt to perform decoding up to 12 times for each of six PDCCHcandidates in the common search space, in consideration of two DCI sizes(DCI formats 0/1A/3/3A and DCI format 1C). In the UE-specific searchspace, the UE needs to attempt to perform decoding for each of 16(6+6+2+2=16) PDCCH candidates up to 32 times, in consideration of twoDCI sizes. Accordingly, when carrier aggregation is not applied, the UEneeds to attempt to perform decoding up to 44 times.

Enhanced Control Channel

Hereinafter, an enhanced PDCCH (EPDCCH) will be described as an exampleof enhanced control channels.

Control information included in the aforementioned DCI formats has beendescribed in terms of a case in which the control information istransmitted through a PDCCH defined in LTE/LTE-A. However, the controlinformation can be applied to another DL control channel, for example,an E-PDCCH in place of the PDCCH. The EPDCCH may correspond to a newform of a control channel for carrying DCI such as scheduling allocationfor the UE and may be introduced in order to effectively support ascheme such as inter-cell interference coordination (ICIC), CoMP,MU-MIMO, etc.

The EPDCCH is differentiated from the existing PDCCH in that the EPDCCHis allocated to a time-frequency resource region (e.g., the data regionof FIG. 3) except for a region (e.g., the control region of FIG. 3)defined for PDCCH transmission in a legacy LTE/LTE-A system(hereinafter, the existing PDCCH will be referred to as a legacy-PDCCHin order to differentiate the PDCCH from the EPDCCH). For example,mapping of resource elements of the EPDCCH may be expressed as mappingthe resource elements to OFDM symbols except for first N (e.g., N≦4)OFDM symbols of a DL subframe in the time domain and mapping theresource elements to a set of semi-statically allocated resource blocks(RBs) in the frequency domain.

For a reason similar to that for introduction of the EPDCCH, an E-PHICHmay be defined as a new control channel for carrying HARQ ACK/NACKinformation about UL transmission and an E-PCFICH may be defined as anew control channel for carrying information about a resource regionused for DL control channel transmission. The EPDCCH, the E-PHICH,and/or the E-PCFICH may be collectively referred to as anenhanced-control channel.

An enhanced REG may be used to define mapping of enhanced-controlchannels to resource elements. For example, for one physical resourceblock (PRB) pair, 16 EREGs (i.e., EREG 0 to EREG 15) may be present. Onone PRB, REs except for REs to which demodulation reference signals(DMRSs) are mapped are denoted by numbers 0 to 15. The numbers areassigned in an order in which frequency increases and then in an orderin which time increases. For example, REs denoted by i constitute EREGi.

Enhanced-control channels may be transmitted using aggregation of one ormore enhanced CCEs (ECCEs). Each ECCE may include one or more EREGs. Thenumber of EREGs per ECCE may be, for example, 4 or 8 (4 in the case of ageneral subframe of a normal CP).

Available ECCEs for the enhanced-control channel may be denoted bynumbers 0 to N_(ECCE)−1. N_(ECCE) may be, for example, 1, 2, 4, 8, 16,or 32.

The number of REs of a PRB pair configured for transmission of theenhanced-control channel may be defined to satisfy the followingconditions i), ii), and iii): i) the REs are contained in one of 16EREGs of the PRB pair; ii) the REs are not used for a cell-specificreference signal (CRS) or a channel state information-reference signal(CSI-RS); and iii) the enhanced-control channel belongs to an OFDMsymbol with an index that is greater than or equal to the index of anOFDM symbol on which a control channel is started.

In addition, enhanced-control channels may be mapped to REs in alocalized manner or a distributed manner. The enhanced-control channelmay be mapped to REs that satisfy the following conditions a) to d): a)the REs are contained in an EREG allocated for transmission; b) the REsare not a part of a PRB pair used in transmitting a physical broadcastchannel (PBCH) or a synchronization signal; c) the REs are not used fora CRS or a CSI-RS for a specific UE; and d) the enhanced-control channelbelongs to an OFDM symbol with an index that is greater than or equal tothe index of an OFDM on which the enhanced-control channel starts.

Allocation of the enhanced-control channel may be performed as thefollowing. One or more enhanced-control channel-PRB-sets may beconfigured for the UE through higher layer signaling from an eNB. Forexample, in the case of the EPDCCH, the enhanced-control channel-PRB-setmay be used for monitoring of the EPDCCH.

In addition, cross interleaving may or may not be applied to mapping ofthe enhanced-control channel to REs.

When cross interleaving is not applied, one enhanced-control channel maybe mapped to a specific set of RBs, and the number of RBs included inthe RB set may correspond to an aggregation level of 1, 2, 4, or 8. Inaddition, another enhanced-control channel may not be transmitted inthis RB set.

When cross interleaving is applied, a plurality of enhanced-controlchannels may be multiplexed and interleaved together and mapped to an RBallocated for enhanced-control channel transmission. That is, multipleenhanced-control channels may also be expressed as being mapped togetherto a specific resource block set.

DCI Format 1A

DCI format 1A refers to DCI formats which are used for compactscheduling of one PDSCH codeword in a cell. That is, DCI format 1A mayinclude control information that is used for rank-1 transmission such assingle antenna transmission, single stream transmission, or transmissiondiversity transmission. Tables 3 and 4 show examples of DCI format 1Athat is defined in the legacy 3GPP LTE/LTE-A standard.

TABLE 6 Carrier Indicator 0 or 3 bits Flag for format 0/format 1Adifferentiation 1 bit Localized/Distributed VRB assignment Flag 1 bitResource Block Assignment N bits Modulation and coding scheme 5 bitsHARQ process number 3 bits (FDD), 4 bits (TDD) New Data Indicator 1 bitRedundancy Version 2 bits TPC (Transmit Power Control) command 2 bitsfor PUCCH Downlink Assignment Index 0 bit (FDD), 2 bits (TDD) SRS(Sounding Reference Signal) request 0 or 1 bit

DCI format 1A containing control information as shown in Table 6 may beprovided to the UE over a PDCCH or an EPDCCH by the eNB.

DCI format 1A contains information for scheduling the most basic DLtransmission (transmission of one PDSCH codeword with rank 1).Accordingly, in the case in which a complex PDSCH transmission schemesuch as transmission with a rank higher than or equal to 2 and/ortransmission of a plurality of codewords is not correctly implemented,DCI format 1A may be used to support the most basic PDSCH transmissionscheme (i.e., fallback).

Quasi Co-Location (QCL)

Hereinafter, a QC or QCL (Quasi Co-Located) relationship will bedescribed in terms of signal or channel.

When large-scale properties of a signal received through one antennaport can be inferred from another signal received through anotherantenna port, the two antenna ports may be said to be QCL. Herein, thelarge-scale properties may include at least one of a delay spread, aDoppler shift, a frequency shift, an average received power, andreceived timing.

Alternatively, two antenna ports may be said to be QCL when large-scaleproperties of a channel over which a symbol on one antenna port istransmitted can be inferred from properties of a channel over whichanother symbol on the other antenna port is transmitted. Herein, thelarge-scale properties may include at least one of a delay spread, aDoppler spread, a Doppler shift, an average gain, and an average delay.

In using the term QC or QCL in this disclosure, the definition thereofis not distinguished in terms of the signals or channels describedabove.

The UE may assume that any two antenna ports having the QCL assumptionestablished therebetween are co-located even if the antenna ports arenot actually co-located. For example, the UE may assume that two antennaports having the QCL assumption established therebetween are at the sametransmission point (TP).

For example, a specific CSI-RS antenna port, a specific downlink DMRSantenna port, and a specific CRS antenna port may be configured to beQCL. This configuration may correspond to a case in which the specificCSI-RS antenna port, the specific downlink DMRS antenna port, and thespecific CRS antenna port are from one serving cell.

Alternatively, a CSI-RS antenna port and a downlink DMRS antenna portmay be configured to be QCL. For example, in a CoMP environment in whicha plurality of TPs participates, a TP from which a CSI-RS antenna portis actually transmitted may not be explicitly known to the UE. In thiscase, the UE may be informed that a specific CSI-RS antenna port and aspecific DMRS antenna port are QCL. This may correspond to a case inwhich the specific CSI-RS antenna port and the specific DMRS antennaport are from a certain TP.

In this case, the UE may increase the performance of channel estimationthrough a DMRS, based on the information about large-scale properties ofa channel acquired using a CSI-RS or a CRS. For example, the UE mayperform an operation of, for example, attenuating interference of achannel estimated through the DMRS, using the delay spread of a channelestimated through the CSI-RS.

For example, regarding delay spread and Doppler spread, the UE may applyestimation results of the power-delay-profile, the delay spread andDoppler spectrum and the Doppler spread for one antenna port to a Wienerfilter which is used in performing channel estimation for anotherantenna port. In addition, regarding frequency shift and receivedtiming, after the UE performs time and frequency synchronization for anantenna port, it may apply the same synchronization to demodulation onanother antenna port. Further, regarding average received power, the UEmay average measurements of reference signal received power (RSRP) overtwo or more antenna ports.

For example, the UE may receive information about a DL scheduling grantthrough a specific DMRS-based DL-related DCI format (e.g., DCI format2C) over a PDCCH (or an EPDCCH). In this case, the UE performs channelestimation of a scheduled PDSCH through a configured DMRS sequence andthen performs data demodulation. For example, if the UE can make a QCLassumption that a DMRS port configuration received from the DLscheduling grant and a port for a specific RS (e.g., a specific CSI-RS,a specific CRS, a DL serving cell CRS of the UE, etc.) are QCL, then theUE may apply the estimates of the large-scale properties such as thedelay spread estimated through the port for the specific RS toimplementation of channel estimation through the DMRS port, therebyimproving performance of DMRS-based reception.

This is because the CSI-RS or CRS is a cell-specific signal transmittedover the full band in the frequency domain, and thus allows for moreaccurate recognition of large-scale properties of a channel than theDMRS. Particularly, the CRS is a reference signal that is broadcast witha relatively high density over the full band in every subframe asdescribed above, and thus, generally, estimates of the large-scaleproperties of a channel may be more stably and accurately acquired fromthe CRS. On the other hand, the DMRS is UE-specifically transmitted onlyon specific scheduled RBs, and accordingly accuracy of estimates of thelarge-scale properties of a channel is lower than in the case of the CRSor the CSI-RS. In addition, even if a plurality of physical resourceblock groups (PBRGs) are scheduled for a UE, an effective channelreceived by the UE may change on a PRBG-by-PRBG basis since a precodingmatrix that the eNB uses for transmission may change on the PRBG-by-PRBGbasis. Therefore, even if large-scale properties of a radio channel areestimated based on the DMRS over a wide band, the accuracy of estimationmay be low.

For antenna ports (APs) which are not QCL (non-quasi-co-located (NQC)),the UE cannot assume that the APs have the same large-scale properties.In this case, the UE needs to perform independent processing for eachNQC AP regarding timing acquisition and tracking, frequency offsetestimation and compensation, delay estimation, and Doppler estimation.

Information indicating whether or not APs are QCL may be provided to theUE through downlink control information (e.g., a PQI field of DCI format2D (a PDSCH RE mapping and QCL indicator field)). Specifically,parameter sets of a QCL configuration may be preconfigured by a higherlayer, and a specific one of the QCL parameter sets may be indicatedthrough the PQI field of DCI format.

Method for Signaling QC-Related Information

According to one embodiment of the present invention, an eNB may signalQC assumption information between RSs such as a CRS, a CSI-RS, and aDMRS, thereby improving performance of CSI feedback and receptionprocessing in the UE.

Higher Layer Signaling of QC-related Information

Hereinafter, descriptions will be given of embodiments of the presentinvention in which QC-related information is configured through higherlayer (e.g., RRC) signaling. For example, when the UE receives signalingof one or more CSI-RS configuration(s) through a higher layer, whetheror not QC assumption with specific RS (s) is possible may be indicatedfor each CSI-RS configuration (herein, the specific RS may be a CRS of aspecific cell (e.g., a DL serving cell or a neighboring cell) of the UE,another CSI-RS, or a DMRS). The UE configured as above may apply such QCassumption or NQC assumption to calculation/determination of information(e.g., RI, PMI, CQI, etc.) to be reported in feeding back CSI based oneach CSI-RS configuration.

As an example of higher layer signaling of QC-related information, anoperation depending on whether QC/NQC assumption between a CSI-RS portand a CRS port is applied will be described.

For example, a UE may receive signaling of a plurality of CSI-RSconfigurations. In the description below, CSI-RS configurations may beunderstood as CSI-RS resources. For example, the UE may receivesignaling of CSI-RS configuration 1 (hereinafter, referred to as“CSI-RS1”) and CSI-RS configuration 2 (hereinafter, referred to as“CSI-RS2”) through a higher layer. In addition, it may be signaled bythe higher layer that it can be assumed that CSI-RS1 and the DL servingcell CRS are QC and that CSI-RS2 and the DL serving cell CRS are NQC.

In this case, the UE may perform CSI calculation using CSI-RS1 for whichQC assumption with the DL serving cell CRS is possible based on thefollowing assumption. In calculating CSI, the UE may calculate/determineRI, PMI, CQI, and the like that do not exceed a predetermined error ratein performing data demodulation on the assumption that a DMRS-basedPDSCH is received. In this case, the UE may calculate an RI, a PMI, aCQI, and the like with which the UE can achieve an FER less than orequal to 10% of the FER obtained in the case of data demodulation on theassumption that a corresponding PDSCH DMRS port(s) has a QC relationshipwith the DL serving cell CRS. In addition, in calculating CSI usingCSI-RS1, the QC assumption may be reflected in a Pc value (see parameterp_C of Table 2) contained in the CSI-RS configuration, in a manner thatpredetermined scaling considering the DL serving cell CRS is applied.

Meanwhile, since CSI-RS2 is configured to have an NQC relationship withthe DL serving cell CRS, the UE does not adopt the QC assumption betweenthe PDSCH DMRS port(s) and the DL serving cell CRS whencalculating/determining RI, PMI and CQI, assuming that a DMRS-basedPDSCH is received from the TP having transmitted CSI-RS2. In otherwords, the UE may calculate/determine an RI, a PMI and a CQI with whichthe UE can achieve an FER less than or equal to 10% of the FER obtainedin the case of data demodulation through the DMRS-based PDSCH withoutthe QC assumption. For example, the UE may calculate/determine an MCSlevel, a CQI, an RI, and the like lower (namely, expected to providemore robust transmission) than when the QC assumption is applicable, andreport the same to the eNB.

As another example of higher layer signaling of QC-related information,information indicating whether or not QC/NQC assumption between CSI-RSport(s) for a specific CSI-RS configuration and CSI-RS port(s) foranother CSI-RS configuration is applied may be included in higher layersignaling.

For example, it is proposed that predetermined location information beincluded in each CSI-RS configuration to be interpreted as indicatingthat QC assumption can be made between CSI-RSs having the same locationvalue. The location information may have a size of N bits. For example,it may be assumed that an eNB having a 2-dimensional uniform rectangularantenna array (URA) including L×M antennas performs 3-dimensionalbeamforming. In this case, the eNB may signal that multiple CSI-RSconfigurations established for one UE by a 2-dimensional URA have a QCrelationship therebetween. Accordingly, the UE may apply part or all oflarge-scale properties (e.g., delay spread, Doppler spread, frequencyshift, received timing, etc.) measured for a specific CSI-RS port forone CSI-RS configuration to a CSI-RS port for another CSI-RSconfiguration. Thereby, channel estimation complexity of the UE may besignificantly reduced. However, if average received powers for differentCSI-RS configurations are assumed to have a QC relationship among otherlarge-scale channel properties, a 3-dimensional beamforming gain may notbe sufficiently achieved. Accordingly, in determining average receivedpower, CSI-RS ports belonging to different CSI-RS configurations may beassumed to have an NQC relationship.

In another example, each CSI-RS configuration may include a flag bit.Every time the flag bit is toggled, it may be indicated whether or not acorresponding CSI-RS configuration belongs to the same group of CSI-RSconfigurations subject to the QC assumption. For example, if the valueof the flag bit is toggled, (namely, if the flag bit of a correspondingCSI-RS configuration changes from 0 to 1 or from 1 to 0 with respect tothe flag bit of the previous CSI-RS configuration), it may be indicatedthat the CSI-RS configuration belongs to a group different from thegroup to which the previous CSI-RS configuration belongs. If the flagbit is not toggled, this may indicate that the CSI-RS configurationbelongs to the group to which the previous CSI-RS configuration belongs.For example, suppose that 5 CSI-RS configurations (CSI-RS1, CSI-RS2, . .. , CSI-RS5) are signaled to the UE and that the flag bits for CSI-RS1and CSI-RS2 are set to ‘0’, flag bits for CSI-RS3 and CSI-RS4 are set to‘1’, and the flag bit for CSI-RS5 is toggled to ‘0’. In this case, itmay be indicated that QC assumption is possible between CSI-RS1 andCSI-RS2 and between CSI-RS3 and CSI-RS4 and that CSI-RS5 does not have aQC relationship with the other CSI-RSs (namely, CSI-RS5 has an NQCrelationship with the other CSI-RSs). Additionally, it can be seen thatQC assumption cannot be made between CSI-RS1 or CSI-RS2 and CSI-RS3 orCSI-RS4.

In another example, when X indicates the value of a CSI-RS sequencescrambling seed included in each CSI-RS configuration, whether or not QCassumption is applied may be implicitly indicated depending on whetheror not the X values are equal. For example, if CSI-RS configurationshave the same X value, it may be indicated that QC assumption is appliedto the CSI-RS port(s) for the CSI-RS configurations. If CSI-RSconfigurations have different X values, it may be indicated that NQCassumption is applied to the CSI-RS port(s) for the CSI-RSconfigurations. Herein, the X value is included in the CSI-RSconfigurations which are UE-specifically established, and accordingly itmay be set independently of a physical cell identifier (PCI), which iscell-specifically given, and be referred to as a virtual cell identifier(VCI). X may be set to an integer between 0 and 503 as in the case ofthe PCI, but need not have the same value as the PCI.

If the value of X included in a specific CSI-RS configuration is equalto the PCI value of specific CRS port(s), it may be implicitly indicatedthat QC assumption may be possible between the CSI-RS port(s) of theCSI-RS configuration and the specific CRS port(s). If the value of Xincluded in a specific CSI-RS configuration is not equal to the PCIvalue of specific CRS port(s), it may be implicitly indicated that NQCassumption may be possible between the CSI-RS port(s) of the CSI-RSconfiguration and the specific CRS port(s).

Additionally, X indicating a CSI-RS scrambling sequence seed value maybe individually allocated to each CSI-RS port in one CSI-RSconfiguration. In this case, whether or not QC/NQC assumption between aCSI-RS port and another RS port (e.g., a CSI-RS port of another CSI-RSconfiguration, another CSI-RS port in the same CSI-RS configuration,and/or a CRS port) is applied may be implicitly indicated depending onwhether the X values of the respective CSI-RS ports (or the X value fora specific CSI-RS port and the PCI value for a specific CRS) are equalto each other.

In another example of higher layer signaling of QC-related information,a specific CSI-RS configuration may contain information indicatingwhether or not QC/NQC assumption between a corresponding port andanother DMRS port is applied.

For example, whether or not QC/NQC assumption specific DMRS port(s) isapplied may be indicated for each CSI-RS configuration through RRC. Ifthe UE receives a configuration of CSI-RS1 to which i QC assumption withall DMRS port(s) is applicable, the UE may apply estimates oflarge-scale properties obtained using CSI-RS1 to DMRS-based PDSCHreception. Upon receiving the configuration of CSI-RS1, the UE mayinterpret this configuration as meaning that the eNB willsemi-statically (namely, as long as the CSI-RS is not reconfigured)transmit a PDSCH to the UE from a TP having transmitted CSI-RS1. Inparticular, in CoMP scenario 4 (i.e., in a situation in which CRSs aresimultaneously transmitted from multiple TPs having the same cell ID),it is difficult to apply a TP-specific QC assumption through such CRSs,and accordingly information about DMRS port(s) for which QC assumptionwith CSI-RS port(s) is established may be signaled to the UE such thatthe information is utilized in improving performance of DMRS-basedreception processing.

In another example, it is assumed that the UE receives configurations ofCSI-RS1 and CSI-RS2 with QC assumption applied between CSI-RS1 and a DLserving cell CRS and NQC assumption applied between CSI-RS2 and the DLserving cell CRS. In this case, the UE may interpret thisreception/operate as having received an implicit semi-static indicationthat QC assumption with both CSI-RS1 and the DL serving cell CRS isapplied to DMRS port(s). For example, as the UE receives a configurationindicating that QC assumption is possible between CSI-RS1 and the DLserving cell CRS, the UE may report, when feeding back CSI based onCSI-RS1, CSI feedback information such as an MCS level and CQI which arehigher than when NQC assumption is established. Accordingly, if the eNBsignals that QC assumption is applied to CSI-RS1 and the DL serving cellCRS (and does not signal otherwise), the UE may interpret this signalingas an agreement that the eNB will cause a TP having transmitted CSI-RS1to transmit a DMRS-based PDSCH when the eNB schedules DL transmissionfor the UE. Thus, the UE may report CSI feedback information based onCSI-RS1 for which QC is assumed, and receive a PDSCH by applying the QCassumption. Thereby, performance of reception processing may beimproved.

Specifically, if any of multiple CSI-RS configurations in a CoMPmeasurement set is allowed to have a QC assumption with the DL servingcell CRS, the UE may implicitly interpret this as semi-staticallyindicating that QC assumption is possible between the corresponding DMRSport(s) and the DL serving cell CRS port(s) of the UE (and CSI-RSport(s) to which QC assumption with the DL serving cell CRS port(s) isapplied) in performing DMRS-based PDSCH demodulation. Thereby, the UE isallowed to perform reception processing in consideration of the QCassumption among the DL serving cell CRS, DMRS and CSI-RS ports. Inaddition, the UE generates CSI to be fed back on the assumption ofreception processing subjected to the QC assumption. For example, the UEmay calculate/determine and report an MCS level, a CQI, an RI, a PMI,and the like with which an error rate less than or equal to 10% can beachieved in performing data demodulation, assuming that the DMRS port(s)has a QC relationship with the DL serving cell CRS port(s) (and CSI-RSport(s) to which QC assumption with the DL serving cell CRS port(s) isapplied) on the assumption that the UE receives a DMRS-based PDSCH.

If all the CSI-RS configurations in a CoMP measurement set are set to besubjected to NQC assumption with the DL serving cell CRS, the UE mayimplicitly interpret this as semi-statically indicating that NQCassumption between the corresponding DMRS port(s) and the DL servingcell CRS port(s) of the UE is applied in performing DMRS-based PDSCHdemodulation. In addition, in performing reception processing, the UEshould not apply the QC assumption between the CSI-RS port(s) of aCSI-RS configuration and other RS port(s). Further, the UE generates CSIto be fed back on the assumption of reception processing subjected tothe NQC assumption. For example, the UE may calculate/determine andreport an MCS level, a CQI, an RI, a PMI, and the like with which anerror rate less than or equal to 10% can be achieved in performing datademodulation, assuming that the DMRS port(s) has an NQC relationshipwith the DL serving cell CRS port(s) on the assumption that the UEreceives a DMRS-based PDSCH.

In another example, when each CSI-RS configuration contains subframeindex information, and a DMRS-based PDSCH is scheduled in correspondingsubframe(s), whether or not QC/NQC assumption between the DMRS port(s)and the CSI-RS port(s) (and the DL serving cell CRS port(s)) is appliedmay be indicated through RRC signaling. For example, if it is signaledthat a QC assumption can be made between CSI-RS1 and the DMRS port(s) ina subframe whose index is an even number, the UE may apply all or someof large-scale properties estimated using CRS port(s)) of CSI-RS1 and/orDL serving cell CRS port(s) to DMRS-based PDSCH reception processing. Infeeding back CSI, the UE may generate and report both CSI inconsideration of QC assumption and CSI in consideration of NQCassumption. Alternatively, the UE may calculate/determine and reportboth a CQI assuming QC and a CQI assuming NQC.

Such signaling may be provided in the form of a subframe bitmap or asubframe index set. For example, subframe set 1 may be configured suchthat the QC assumption is possible between DMRS port(s) and DL servingcell CRS port(s), and subframe set 2 may be configured such that the QCassumption is possible between DMRS port(s) and specific CSI-RS port(s).Alternatively, subframe set 1 may be configured such that the QCassumption is possible between DMRS port(s) and DL serving cell CRSport(s), and subframe set 2 may be configured such that DMRS port(s) andspecific CSI-RS port(s) are assumed to be NQC.

Dynamic Signaling of QC-Related Information

Hereinafter, description will be given of examples of the presentinvention of configuring QC-related information through dynamicsignaling. For example, the UE may receive DL-related (or downlinkgrant) DCI about DMRS-based PDSCH transmission through a PDCCH or anEPDCCH. The DCI may include information indicating whether or not QCassumption between DMRS port(s) and other RS (e.g., a DL serving cellCRS or CSI-RS of the UE) port(s) is applied.

As an example of dynamic signaling of QC-related information, onlywhether or not QC assumption is made between the DMRS port(s) and aspecific RS (e.g., the DL serving cell CRS or CSI-RS of the UE) port(s)may be dynamically signaled through information having the size of 1bit. Thereby, if a PDSCH is transmitted, in the manner of dynamic pointselection, from a TP for which QC assumption is possible when DL-relatedDCI for PDSCH scheduling in a manner of CoMP DPS or dynamic cellselection, the eNB may signal, to the UE, that application of QCassumption is possible, thereby improving performance of receptionprocessing of the UE.

In another example of dynamic signaling of QC-related information,“QC-pair information between a CSI-RS port and a DMRS port” or “QC-pairinformation between a CRS port and a DMRS port” may be semi-staticallypre-configured as information having a plurality of states by higherlayer (e.g., RRC layer) signaling, and one of the states may bedynamically indicated when scheduling grant information is provided tothe UE through DCI. For example, one of N (e.g., N=2) bit states isdynamically triggered, and each of the states corresponds to one ofinter-RS QC-pair candidates (e.g., a pair of a CSI-RS and a DMRS and apair of a CRS and a DMRS) pre-configured by RRC.

For example, if N=2, states may be pre-configured such that state ‘00’indicates NQC (namely, DMRS ports are not subject to QC assumption withother RS ports), state ‘01’ indicates that QC assumption with a DLserving cell CRS port is possible, state ‘10’ indicates that QCassumption with a first RRC-configured set of RS (e.g., specific CSI-RSor specific CRS) ports is possible, and state ‘11’ indicates that asecond RRC-configured set of RS ports configured by RRC is possible. Forexample, the inter-RS QC-pair of the first RRC-configured set mayindicate that “DMRS ports can have QC assumption with CSI-RS port(s) ofCSI-RS1 and CSI-RS2”, and the second RRC-configured inter-RS QC-pair mayindicate that “DMRS ports can have QC assumption with CRS port(s)”.

In addition, QC information and CRS rate matching (RM) patterninformation may be jointly encoded. In this case, the N bit field in theDCI format may be referred to as a “PDSCH RE mapping and QCL indicatorfield” (or PQI field).

For example, N (e.g., N=2) bit states may be configured as shown inTable 7 below.

TABLE 7 QC assumption RM pattern information Flag for QC State withCSI-RS (RM pattern information) assumption with CRS ‘00’ CSI-RS1 CRS-RM1(e.g., PCI1) 1 ‘01’ CSI-RS2 CRS-RM2 (e.g., PCI2) 1 ‘10’ CSI-RS3 CRS-RM3(e.g., PCI3) 0 ‘11’ CSI-RS1, CRS-RM1 (e.g., PCI1), 1 CSI-RS2 CRS-RM2(e.g., PCI2)

In Table 7, the item “QC assumption with CSI-RS” indicates a CSI-RSconfiguration to which QC assumption with the DMRS port is applicablewhen information indicating a specific state (‘00’, ‘01’, ‘10’, ‘11’) isincluded in DL-related DCI for scheduling transmission of a DMRS-basedPDSCH. For example, it may be assumed that one different CSI-RS per TPis pre-configured for the UE through RRC signaling. Herein, a specificTP may be referred to as TPn with an index n(n=0, 1, 2, . . . ), aCSI-RS configuration corresponding to TPn may be referred to as CSI-RSn.Herein, the term TP may be understood as meaning a cell. CSI-RSn may bea CSI-RS configuration of non-zero Tx power (non-zero power (NZP)).

In this case, state ‘00’ of Table 7 may indicate that QC assumptionbetween CSI-RS port(s) for CSI-RS1 transmitted from TP1 and the DMRSport(s) is possible. State ‘01’ may indicate that QC assumption ispossible between CSI-RS port(s) of CSI-RS2 transmitted from TP2 andcorresponding DMRS port(s), and state ‘10’ may indicate that QCassumption is possible between CSI-RS port(s) of CSI-RS3 transmittedfrom TP3 and corresponding DMRS port(s). That is, the eNB may indicateone of states ‘00’, ‘01’ and ‘10’ through the DL-related DCI, therebydynamically signaling DPS-wise PDSCH transmission from one of TP1, TP2and TP3.

The item “QC assumption with CSI-RS” of Table 7 may also be signaled,for example, in a manner of informing that the CSI-RS is transmittedfrom specific TP(s). For example, the UE may be informed of a TPtransmitting a CSI-RS to which QC assumption with the DMRS is applied,using an identifier (e.g., PCI, VCI, a scrambling sequence seed value,or the like) configured to indicate specific TP(s).

The item “QC assumption with CSI-RS” may also be used to indicate aspecific CSI process. In the case of DPS-wise PDSCH transmission, onlyone CSI process index may be indicated. In the case of PDSCHtransmission in the JP or joint transmission (JT) scheme, multiple CSIprocess indexes may be indicated. Each CSI process may be associatedwith a CSI-RS resource for channel measurement and a CSI-interferencemeasurement resource (CSI-IM resource). Specifically, one CSI process isdefined to be associated with an NZP CSI-RS resource for measurement ofa desired signal and an interference measurement resource (IMR) forinterference measurement. Each CSI process has an independent CSIfeedback configuration. The independent CSI feedback configurationrepresents a feedback mode (the type of CSI (RI, PMI, CQI, etc.) and atransmission order of CSIs), a periodicity of feedback and a feedbackoffset.

When N (N=2) bit information indicating “QC assumption with CSI process”is included in DL-related DCI for scheduling DMRS-based PDSCHtransmission as described above, the information may indicate whether QCassumption with the DMRS is applicable for each of the NZP CSI-RSresource and the IMR which are associated with a specific CSI process.That is, information indicating whether QC assumption with the DMRS isapplicable to both the NZP CSI-RS resource and the IMR, to only the NZPCSI-RS resource, or to only the IMR, or whether both are NQC with theDMRS may be individually provided.

If QC assumption is applicable between the IMR and the DMRS, this maymean that a parameter (e.g., the value of interference or noisevariance) estimated through the IMR is allowed to be utilized todetermine a coefficient of a minimum mean squared error (MMSE) filtersuch as the Wiener filter in the reception processing for DMRS-baseddemodulation. In this case, performance of demodulation of the DMRS maybe improved.

By individually signaling whether or not QC assumption with the DMRS isapplicable for each of the NZP CSI-RS and the IMR associated with a CSIprocess, more accurate channel estimation may be expected. For example,when a parameter (e.g., noise variance value) estimated using the IMR isused for reception processing for data demodulation based on the DMRS(e.g., when the parameter is used as a coefficient of an MMSE filter),there may occur an error in single-user (SU)-MIMO transmission ormultiple user (MU)-MIMO transmission. Specifically, for SU-MIMOtransmission, QC assumption with the DMRS is applicable for both the NZPCSI-RS resource and the IMR, and thus it may be expected that datademodulation performance will be improved. For MU-MIMO transmission, onthe other hand, QC assumption with the DMRS is preferably applicableonly to the NZP CSI-RS resource and NQC assumption is establishedbetween the IMR and the DMRS (namely, a value such as noise varianceestimated using the IMR is prohibited from being reused for datademodulation).

Accordingly, an additional flag bit with the size of 1 bit operativelyconnected with each state of Table 7 may be defined such that the flagbit indicates only QC assumption between an NZP CSI-RS resource and theDMRS when the flag bit is set to ‘0’, and indicates QC assumptionbetween the DMRS and both the NZP CSI-RS resource and the IMR when theflag bit is set to ‘1’. Alternatively, the additional flag bit may bedefined such that the flag bit indicates MU-MIMO transmission when setto ‘0’, and indicates SU-MIMO transmission when set to ‘1’.Alternatively, the additional flag bit may be defined such that the flagbit indicates, when set to ‘0’, that QC assumption between a CSI processindex and the DMRS is disabled (namely, NQC assumption is applied), andindicates, when set to ‘1’, that the QC assumption between the CSIprocess index and the DMRS is enabled.

The N bit (e.g., N=2) information and/or the additional flag informationwith the size of 1 bit which is defined for dynamic signaling of QCinformation as described above may reuse a format defined in the legacyDCI format, or a new bit field may be additionally defined. When theadditional flag information with the size of 1 bit is used to switchon/off the QC assumption depending on whether MIMO is SU-MIMO orMU-MIMO, the information may be semi-statically configured as additionalinformation indicated by the N bit information (namely, informationwhich each state of the N bit information pre-represents through RRCsignaling), rather than being included in dynamic signaling as aseparate bit.

In the example of Table 7, a TP implementing PDSCH transmission in theDPS scheme (or an RS to which QC assumption with the DMRS is applied)may be indicated as described above. Additionally, as in the case ofstate ‘11’ of Table 7, PDSCH transmission from TP1 and TP2 in the JTscheme may be indicated. That is, as in the example of Table 7, the item“QC assumption with CSI-RS” may be signaled as “CSI-RS1, CSI-RS2”, as anidentifier corresponding to TP1 and TP2 (e.g., PCI, VCI, or a scramblingsequence seed value), or as “CSI process1, CSI process2”. Once the UEacquires such signaling information through DCI, the UE may recognize,through information indicating that QC assumption with TPs isapplicable, that DMRS ports will be transmitted from multiple TPs in theform of a virtual DMRS, and may determine estimates of large-scaleproperties from the TPs by averaging estimates of large-scale propertiesfrom the TPs and use the same to improve reception performance.

In another example, the item “QC assumption with CSI-RS” for a specificstate (e.g., state ‘11’ of Table 7) in the N bit information may be setto “non-QC (NQC)” or “not available” or left empty to signal that QCassumption with any TPs should not be applied. This may be used toindicate JT. For example, in the case of JT, since providing onlyinformation about QC assumption with one specific TP may beinappropriate, the NQC state may be signaled. If “not available” orempty item is signaled, the NQC state may be implicitly indicated, andas a result no QC assumption may be applied or a certain default statemay be applied. For example, the default state may be defined as a statein which only QC assumption with a specific DL serving cell RS(s) (e.g.,a DL serving cell CRS, a CSI-RS corresponding to a default TP (e.g., aDL serving TP), a CSI-RS belonging to a specific CSI process, etc.) canbe applied.

Additionally, as in the example of Table 7, information about a CRS ratematching (RM) pattern which the UE needs to assume upon receiving acorresponding PDSCH may be signaled. The information about the CRS RMpattern may include the number of CRS ports, a CRS v-shift (a value ofshift in the frequency axis with respect to a basic CRS pattern (seeFIG. 6)), and a subframe set to which the RM pattern is applied. The CRSRM pattern refers to configuring PDSCH symbols on the assumption that aPDSCH is mapped to the REs except RE(s) to which a CRS is mapped.Accordingly, a terminal that receives the PDSCH can correctly demodulatethe PDSCH only when it correctly recognizes a CRS pattern which isconsidered in rate-matching and transmitting the PDSCH.

For example, when CRS RM pattern information which TPn transmits isdefined as CRS-RMn, state ‘00’ may signal CRS-RM1 representinginformation about a CRS RM pattern transmitted from TP1, state ‘01’ maysignal CRS-RM2 representing information about a CRS RM patterntransmitted from TP2, and state ‘10’ may signal CRS-RM3 representinginformation about a CRS RM pattern transmitted from TP3. That is, theeNB may indicate one of states ‘00’, ‘01’ or ‘10’, thereby dynamicallysignaling PDSCH transmission according to DPS from one of TP1, TP2 andTP3. Herein, each CRS RM pattern may be correctly and dynamicallyindicated in the form of CRS-RMn by providing CRS RM pattern informationin addition to “QC assumption with CSI-RS” information, particularly inCoMP scenario 3 (namely, in a situation in which CRSs are simultaneouslytransmitted from multiple TPs having different cell IDs (i.e., PCIs).

Each pattern may also be signaled in a manner of informing that the item“RM pattern information” of Table 7 is transmitted from specific TP(s).For example, the UE may be informed of a CRS RM pattern by using anidentifier (e.g., a PCI, a VCI, or a scrambling sequence seed value,etc.) indicating specific TP(s).

As described above, DPS transmission may be dynamically indicatedthrough state ‘00’, ‘01’ or ‘10’. Additionally, as a method forindicating JT from TP1 and TP2 as in the example of state ‘11’ of Table7, the item “RM pattern information” may be signaled as “CRS-RM1,CRS-RM2”, or an identifier (e.g., PCI, VCI, or scrambling sequence seedvalue, etc.) corresponding to TP1 and TP2 may be indicated. The UEhaving acquired such signaling information through DCI may perform PDSCHdemodulation, assuming, for example, that PDSCHs are rate-matched on allREs corresponding to a union of CRS-RM1 and CRS-RM2. That is, ifmultiple pieces of CRS RM pattern information are indicated by the item“RM pattern information”, the UE receiving the PDSCH may perform PDSCHdemodulation, assuming that the PDSCH is not mapped to RE positionsindicated by any one of indicated CRS RM patterns (namely, rate-matchingis performed during PDSCH transmission).

Additionally, as in the example of Table 7, the item “Flag for QCassumption with CRS” may include flag indication information indicatingwhether or not QC assumption can be established between specific CSI-RSnindicated by the item “QC assumption with CSI-RS” and a specific CRSport (i.e., CRS port(s) designated by PCI information) indicated by theitem “RM pattern information”. Specifically, if a specific state value(e.g., ‘00’, ‘01’, ‘10’, ‘11’) is triggered and the flag bit in theinformation indicated by the state value is enabled (or is set to ‘1’),this may be defined to indicate that QC assumption can be establishedbetween CSI-RS port(s) of CSI-RSn indicated by the state value and CRSport(s) of CRS-RMn indicated by the state value (the CRS port(s) may beknown, for example, through PCIn or VCIn which the CRS-RMn indicates).If a specific state value (e.g., ‘00’, ‘01’, ‘10’, ‘11’) is triggeredand the flag bit in the information indicated by the state value isdisabled (or set to ‘0’), this may be defined to indicate that QCassumption should not be established between CSI-RS port(s) of CSI-RSnindicated by the state value and CRS port(s) of CRS-RMn indicated by thestate value (the CRS port(s) may be known, for example, through PCIn orVCIn which the CRS-RMn indicates) (namely, an NQC relationship isestablished).

Referring to Table 7, states ‘00’ and ‘01’ have “Flag for QC assumptionwith CRS” set to ‘1’, and thus respectively indicate DPS transmissionfrom TP1 and TP2. Specifically, if the flag bit is set to ‘1’ in state‘00’, this is interpreted as indicating that QC assumption betweenCSI-RS1 and DMRS port(s) and QC assumption between CSI-RS1 andPCI1-based CRS port(s) are applicable on the assumption that a PDSCH israte-matched according to CRS-RM1 pattern. If the flag bit is set to ‘1’in state ‘01’, this is interpreted as QC assumption between CSI-RS2 andDMRS port(s) and QC assumption between CSI-RS2 and PCI2-based CRSport(s) are applicable on the assumption that a PDSCH is rate-matchedaccording to CRS-RM2 pattern.

If not only applicability of QC assumption between DMRS port(s) andspecific CSI-RS port(s) but also applicability of QC assumption betweenCSI-RS port(s) and specific CRS port(s) (i.e., information indicated bythe flag bit of Table 7) is signaled to the UE as above, the UE may beallowed to use not only CSI-RS port(s) to which QC assumption isapplicable, but also large-scale channel properties estimated from theCRS port(s) providing a significantly high RS density (namely, moreaccurate large-scale channel properties) in performing DMRS-based PDSCHdemodulation.

Meanwhile, in the example of Table 7, if “Flag for QC assumption withCRS” corresponding to state ‘10’ is set to ‘0’, which indicates DPStransmission from TP3, this is interpreted as meaning that QC assumptionbetween CSI-RS3 and DMRS port(s) is applicable, but QC assumptionbetween CSI-RS3 and PCI3-based CRS port(s) should not be applied on theassumption that a PDSCH is rate-matched according to CRS-RM3 pattern.

In the example of Table 7, if “Flag for QC assumption with CRS”corresponding to state ‘11’ is set to ‘1’, which indicates JTtransmission from TP1 and TP2, this is interpreted as meaning that QCassumption between CSI-RS1 and PCH-based CRS port(s) and QC assumptionbetween CSI-RS2 and PCI2-based CRS port(s) are applicable on theassumption that a PDSCH is rate-matched in consideration of both CRS-RM1and CRS-RM2 patterns.

If multiple CSI-RSn's are present in the item “QC assumption withCSI-RS” corresponding to a specific state, and CRS-RMn's are present inthe item “RM pattern information”, this may be interpreted as meaningthat QC-pairs between a CSI-RSn and a CRS-RMn are configured in apredetermined order. For example, this case may be interpreted asmeaning that QC assumption between CSI-RS1 and CRS-RM1 and QC assumptionbetween CSI-RS2 and CRS-RM2 is applied. If the flag bit is set to ‘0’,for example, this may be interpreted as meaning that neither QCassumption between CSI-RS1 and CRS-RM1 nor QC assumption between CSI-RS2and CRS-RM2 is applied (namely, an NQC relationship is establishedbetween the CSI-RSs and the CRS-RMs). Alternatively, “Flag for QCassumption with CRS” information may be configured in a manner such thatthe information individually indicates whether QC/NQC is establishedbetween each CSI-RSn and each CRS-RMn.

As another example of dynamic signaling of QC-related information, N(e.g., N=2) bit states may be configured as shown in Table 8.

TABLE 8 QC assumption Flag for QC with RM pattern assumption StateCSI-RS) information with CRS Interpretation ‘00’ CSI-RS1 CRS-RM4 0 Thereis no CRS port (e.g., PCI4) to which QC assumption with CSI- RS1 isapplicable (NQC). ‘01’ CSI-RS2 CRS-RM4 0 There is no CRS port (e.g.,PCI4) to which QC assumption with CSI- RS1 is applicable (NQC). ‘10’CSI-RS3 CRS-RM3 1 QC assumption (e.g., PCI3) between CSI-RS3 and aPCI3-based CRS port is applicable. ‘11’ CSI-RS1, No-CRS 0 There is noCRS port CSI-RS2 (i.e., to which QC MBSFN) assumption with CSI- RS1 andCSI-RS2 is applicable (NQC).

In the example of Table 8, CRS-RM4 (e.g., PCI4) may correspond to CoMPscenario 4, in which TP1 and TP2 share PCI4. In addition, as in the caseof state ‘11’ of Table 8, No-CRS (i.e., MBSFN) may be indicated as CRSRM pattern information. Referring to FIG. 3, an MBSFN subframe mayrepresent a subframe in which only a CRS and a control channel (e.g.,PDCCH) are transmitted in the control region, and neither the CRS northe PDSCH is transmitted in the data region. To perform scheduling of JTonly in MBSFN subframes, No-CRS (i.e., an MBSFN) may be indicated. TheUE may interpret this indication as meaning that there is no CRS in thedata region, and thus may assume that rate matching of the PDSCH is notperformed at RE locations corresponding to CRS ports (namely, the PDSCHis mapped to the corresponding REs) in assuming rate matching for thePDSCH.

The DMRS scrambling seed value x(n) (e.g., n=0, 1) may be implicitlypre-linked or pre-tied (e.g., by RRC signaling) to each state of an Nbit-sized field (e.g., a PQI field) described above with reference toTables 7 and 8. In this case, when a specific one of 2̂N states isindicated by dynamic signaling, a joint encoding scheme may be used, forexample, in a manner that a separate dynamic indication parameter (e.g.,a scrambling identifier (nSCID)) indicates a value to be used among thevalues of x(n) linked to the state.

In the case in which the joint encoding scheme described above is addedto the example of Table 7, an example of Table 9 below may beconsidered.

TABLE 9 QC Flag for DMRS DMRS assump- QC scrambling scrambling tionassump- seed x(0) seed x(1) with RM pattern tion tied to tied to StateCSI-RS information with CRS nSCID = 0 nSCID = 1 ‘00’ CSI-RS1 CRS-RM1 1315 420 (e.g., PCI1) ‘01’ CSI-RS2 CRS-RM2 1 96 420 (e.g., PCI2) ‘10’CSI-RS3 CRS-RM3 0 117 420 (e.g., PCI3) ‘11’ CSI-RS1, CRS-RM1 1 480 420CSI-RS2 (e.g., PCI1), CRS-RM2 (e.g., PCI2)

In the example of Table 9, the range of x(n) may be from 0 to 503, whichcorresponds to the PCI range. Table 9 shows exemplary values of x(0) andx(1) allocated to each state. For example, 420 may be allocated incommon as a value of x(1) linked/tied to nSCID=1. If a specificidentifier value to be used in common by multiple TPs is allocated andnSCID=1 is indicated as in this case, using the shared identifier valuemay be allowed, thereby ensuring DMRS orthogonality between TPs. Inaddition, different values of x(0) linked/tied to nSCID=0 may beallocated to the individual states as in the example of Table 9.Thereby, a TP-specific VCI (or a scrambling seed value) may be used toacquire a cell-splitting gain. In addition, a separate VCI (orscrambling seed value) for JT may be designated by allocating a value ofx(0) to state ‘11’ such that the value of x(0) for state ‘11’ differsfrom the values of x(0) for the other states as in the example of Table9.

For example, different values of x(n) may be linked/tied to 2̂N statesrespectively in an N bit field (e.g., a PQI field) indicating QCinformation and information about a CRS RM pattern as described above.In this case, the value of nSCID to be used to generate a DMRS sequenceis dynamically indicated through another filed in the DCI format, andthe value of x(n) is implicitly determined according to the value ofnSCID. For example, a rule may be established such that x(n) (e.g., n=0or 1) is indicated when nSCID=n. For example, when a specific state ofthe 2̂N states is dynamically indicated, x(0), x(1), and the like linkedto the state are determined through joint encoding for x(n).Additionally, one of x(0), x(1), and the like is finallydetermined/selected according to the value of nSCID indicated through aseparate field.

QC Behavior

In a legacy system (e.g., a system operating according to a standardprior to 3GPP LTE Release-10 (Rel-10)) that does not support CoMPoperation, a behavior of assuming QC between RS ports may besubstantially viewed as being implicitly defined. In this invention,this behavior may be referred to as Behavior A. Behavior A may bedefined as a behavior of assuming that a CRS, a CSI-RS and a PDSCH DMRSare QC with respect to at least one of frequency shift, Doppler spread,received timing and delay spread. This is because the CRS port, CSI-RSport and the PDSCH DMRS port all naturally need to be assumed to betransmitted from one cell or TP in the legacy system, withoutconsidering CoMP operation.

In a system supporting CoMP operation, another behavior (e.g., abehavior of assuming that CSI-RS1 of TP1 and CSI-RS2 of TP2 are QC) maybe defined for QC assumption. Accordingly, an embodiment of the presentinvention proposes that Behavior A be defined as a default behavior in asystem to which multiple QC behaviors are applicable. That is, the UEmay be defined to always operate according to Behavior A, which is thedefault behavior, if a specific condition is satisfied.

For example, the UE may be configured to always apply Behavior A tospecific CSI process index(s) unless the index is not separatelysignaled. This is intended to ensure the same performance as in thelegacy system (Rel-10 system) by allowing the UE to operate according tothe same QC assumption as in the legacy system for at least one CSIprocess when multiple CSI processes are configured for the UE. Forexample, for CSI process index 0, Behavior A may always be applied. Inthis case, a specific CSI-RS resource to which QC assumption with a CRStransmitted from a DL serving cell/TP is applicable in, for example,CoMP scenario 3, may be configured for CSI process index 0.

Behavior A, which is the default behavior, may be defined to be appliedto transmission modes (e.g., TM9) defined in a legacy system (e.g., asystem operating according to a standard prior to 3GPP LTE Rel-10) otherthan a new transmission mode (e.g., TM10) defined in a CoMPoperation-supporting system (e.g., a system conforming to a standardafter 3GPP LTE Rel-11).

A QC behavior applicable to only a system supporting the CoMP operationmay be defined as follows.

In the case in which a DL grant is received through a DCI format (e.g.,DCI format 2D) applied to a new transmission mode (e.g., TM10), the UEmay assume a new QC behavior (hereinafter, Behavior B). Behavior B maybe defined as assuming that a CRS, a CSI-RS, and a PDSCH DMRS (and/or anEPDCCH DMRS) are not QC with respect to at least one of delay spread,Doppler spread, Doppler shift, average gain, and average delay, exceptfor the following exception. The exception is that a PDSCH DMRS (and/oran EPDCCH DMRS) and a specific CSI-RS resource indicated by physicallayer signaling (e.g., signaling through PDCCH DCI) can be assumed to beQC with respect to at least one of the delay spread, the Doppler spread,the Doppler shift, and the average delay. That is, Behavior B may bebasically configured not to allow QC assumption between a CRS andanother RS (e.g., a CSI-RS and a DMRS), and when the DL grant isreceived through DCI format 2D, QC assumption between CSI-RS port(s) ofa specific CSI-RS resource indicated by dynamic signaling as in theexamples of Tables 7, 8 and 9 and DMRS port(s) of a PDSCH scheduled byDCI format 2D may be applicable.

Whether or not QC assumption between a specific CRS and a specificCSI-RS is applicable may also be signaled in the examples of Tables 7, 8and 9 (or through separate RRC signaling).

If the DL grant is received through DCI format 2D, QC assumption betweena corresponding PDSCH DMRS port and a specific CSI-RS port may beestablished. Additionally, whether or not QC assumption between aspecific CSI-RS and a specific CRS is applicable may be configuredthrough RRC signaling. In this case, it may be signaled that QCassumption can be established among a DMRS port, a CSI-RS port and a CRSport. Behavior B may be given for DCI format 2D, and the UE may performdata demodulation (for example, the UE may reflect large-scaleproperties estimated through other RSs in determining a Wiener filtercoefficient) based on the QC assumption according to Behavior B. WhenBehavior B is applied, a specific CSI-RS, a CRS, and a DMRS are notnecessarily from the DL serving cell even if it is indicated that QCassumption has been established among the specific CSI-RS, the CRS, andthe DMRS, which is a great difference from Behavior A. For example, theCRS may correspond to a CRS port of a neighboring cell rather than theDL serving cell, and one of multiple CSI-RS resources may be indicatedfor the CSI-RS.

Regarding frequency offset (or Doppler shift), even if the UE is set toBehavior B, it may be configured to estimate an initial (or coarse)frequency offset based on the serving cell CRS and to estimate a finefrequency offset through an indicated CSI-RS only within a specificfrequency range (e.g., [−N; +N] Hz). For example, if the transmissionperiodicity of the CSI-RS is 5 ms, the frequency offset of 200 Hz, whichis the reciprocal of 5 ms, may be estimated based on the CSI-RS withoutambiguity, and thus the following operation of the UE may be defined.

The UE may expect, using the CSI-RS as indicated (by Behavior B), that aDoppler shift (and/or Doppler spread) tracked by the UE is within therange of frequency offset (e.g., [−N; +N] Hz) for the serving cell. Forexample, if the periodicity of the indicated CSI-RS is 5 ms, N=100 Hz.If the periodicity of the indicated CSI-RS is 10 ms, N=50 Hz. If theperiodicity of the indicated CSI-RS is 20 ms, N=25 Hz. If theperiodicity of the indicated CSI-RS is 40 ms, N=12.5 Hz. If theperiodicity of the indicated CSI-RS is 80 ms, N=6.25 Hz. Briefly, if theindicated CSI-RS has a periodicity of T [ms], N may be set such thatN=1/(kT) [Hz]. Herein, k may be, for example, 2.

The proposed embodiment of the present invention above means that the UEvariably determines a frequency range to be searched with respect to theserving cell CRS for estimation of a frequency offset (or a Dopplershift and/or a Doppler spread) as the periodicity of the indicatedCSI-RS varies. Herein, the indicated CSI-RS may represent one NZP CSI-RSwhich can establish QC assumption with a DMRS indicated by a DCI (e.g.,DCI format 2D) in the case of a UE for which a plurality of CSI-RSresources are configured by a higher layer (e.g., a UE for which TM10 isconfigured). Alternatively, the indicated CSI-RS may be a specificdefault CSI-RS configured through RRC in the case of DCI format 1A.

If the periodicity of the CSI-RS is 10 ms, the range for the UE tosearch is reduced by half of the range for the periodicity of 5 ms. Thatis, as the CSI-RS periodicity set by the eNB increases, the frequencyoffset between the CSI-RS and the CRS of a serving cell needs to be setwithin a narrower range. In this case, the UE only needs to estimate thefrequency offset within a narrower search range. To prevent CSI-RStransmission having a frequency offset out of the search range fromcausing the UE to incorrectly perform channel estimation and degradingthe performance of the UE, the eNB needs to ensure the relationshipbetween the CRS and the CSI-RS as above.

In view of the eNB, if a frequency offset (or a Doppler shift) betweenthe oscillator of a TP transmitting the CRS and the oscillator of a TPtransmitting the indicated CSI-RS is not within a range of [−N; +N] Hzaccording to N=1/(kT) (e.g., k=2) corresponding to the periodicity ofthe indicated CSI-RS, T[ms], this may mean that the periodicity of theCSI-RS cannot be set to T [ms]. In this case, the eNB needs to configureand transmit a CSI-RS having a periodicity set to a value less than T[ms].

Alternatively, to unify the UE operations, the eNB may be limited toalways configure only a CSI-RS having the periodicity of T1 ms (e.g.,T1=5) as a CSI-RS to be applied to the case of Behavior B. In this case,the UE may expect that the Doppler shift (and/or Doppler spread) trackedby the UE by using the CSI-RS as indicated (Behavior B) is within therange of frequency offset ([−N; +N] Hz with, for example, N=100) withrespect to the serving cell, regardless of the indicated periodicity ofthe CSI-RS.

Alternatively, the eNB may configure a CSI-RS having a periodicitydifferent from the periodicity of T1 ms, but may set the frequency rangefor the UE to search to the narrowest range. For example, the eNB mayconfigure various CSI-RSs having periodicities of T=5, 10, 20, 40 and 80ms, such that the value of N always ensures at least the narrowest range(namely, N=6.25 Hz when T=80 ms). In this case, the UE may expect thatthe Doppler shift (and/or Doppler spread) tracked by the UE by using theCSI-RS as indicated (Behavior B) is within the range of frequency offset([−N; +N] Hz with, for example, N=6.25) with respect to the servingcell, regardless of the indicated periodicity of the CSI-RS. If the eNBcan configure various CSI-RSs having periodicities of T=5 and 10, N maybe set to 50 Hz to ensure the narrowest frequency range of search. Thatis, regardless of the periodicity of the indicated CSI-RS, the UE mayonly need to perform search within a specific range of [−N; +N] Hz.Thereby, the eNB may configure only a CSI-RS having a periodicityensuring the above operation of the UE such that the UE utilizes theCSI-RS in Behavior B.

If system performance is lowered or other problems occur in a system towhich a new transmission mode (e.g., TM10) is applicable, operation inthe default transmission mode needs to be supported for stableoperation. This mode may be referred to as a fallback operation mode.For example, in the case in which a DL grant is received through afallback DCI format (e.g., DCI format 1A) in MBSFN subframes, the UE mayoperate according o to Behavior A′ (i.e., a variant of Behavior A).Behavior A′ may be defined as assuming that a CRS, a CSI-RS, and a PDSCHDMRS (and/or an EPDCCH DMRS) are not QC with respect to at least one ofdelay spread, Doppler spread, Doppler shift, average gain, and averagedelay, except for the following exception. The exception may be that aCRS (e.g., a CRS of a DL serving cell or a specific CRS indicatedthrough RRC signaling) and a PDSCH DMRS are assumed to be QC withrespect to at least one of the delay spread, the Doppler spread, theDoppler shift, and the average delay. That is, Behavior A′ may bebasically configured not to allow QC assumption between a CSI-RS andanother RS (e.g., a CRS, a DMRS), and when the DL grant is receivedthrough DCI format 1A in an MBSFN subframe, QC assumption may be alwaysestablished between specific CRS port(s) and DMRS port(s) (e.g., DMRSport 7) of a PDSCH scheduled by DCI format 1A.

In another example, Behavior A′ may be defined such that QC assumptioncan be additionally established between a specific CSI-RS resource indexn (e.g., n=0), a CRS and a DMRS. In this case, the scrambling seed valueX of the corresponding CSI-RS resource may be restricted to be always aPCI. Alternatively, it may be expressed in terms of operation of the UEthat the UE is not allowed to expect that CSI-RS resource index n is notidentical to the PCI. Alternatively, a CSI process (or a specific CSI-RSresource associated with the CSI process) may be used in place of theCSI-RS resource. That is, Behavior A′ may be presented as indicatingthat additional QC assumption can be established between specific CSIprocess i (e.g., i=0), a CRS and a DMRS. When the UE performs datademodulation according to the above assumption, it may apply large-scalechannel properties estimated using other RSs to a reception process (by,for example, determining a Wiener filter coefficient based on theproperties).

As Behavior A′ is defined as a separate behavior different from BehaviorA or B as above, performance of data demodulation of the UE may befurther improved. Specifically, DCI format 1A, which corresponds to afallback DCI format, may be used to ensure clear and robusttransmission, for example, in a situation in which ambiguity can occurin a period in which various RRC reconfigurations are applied. In alegacy system (e.g., a Rel-10 system), demodulation is defined to beperformed through DMRS port 7 when DCI format 1A is received in an MBSFNsubframe. In performing demodulation, a PCI may be used as a DMRSscrambling seed. In this case, QC assumption may be established betweena DL serving cell CRS port through which a CRS generated using the PCIis broadcast and a DMRS. Accordingly, more accurate large-scale channelproperties measured using the CRS can be used in performing datademodulation, thereby improving data demodulation performance.

Accordingly, Behavior A′ may basically allow QC assumption between a CRSport and a DMRS port. In addition, Behavior A′ may provide informationindicating that QC assumption can be established between a specificCSI-RS resource index (e.g., CSI-RS resource index 0) or a CSI-RS portbelonging to the specific CSI process index (e.g., CSI process index 0)and a DMRS port. For example, in CoMP scenario 4, in which multiple TPsuse the same cell identifier, CSI-RSs may be simultaneously transmittedfrom the TPs from which CRSs are simultaneously transmitted (namely,virtual CSI-RSs generated by the PCI may be simultaneously transmittedfrom a plurality of TPs).

In other words, Behavior A′ may be understood as being basically similarto Behavior A in that QC assumption can always be established between aCRS and a DMRS, but being different from Behavior A in terms of a methodof indicating a CSI-RS to which QC assumption with a DMRS is applicable.Specifically, according to Behavior A, a CSI-RS to which QC assumptionwith a DMRS is applicable may be dynamically indicated through the DCI.According to Behavior A′, on the other hand, a CSI-RS to which QCassumption with the DMRS is applicable may be semi-statically indicatedthrough RRC signaling or a specific CSI-RS resource index (e.g., CSI-RSresource index 0) may be statically configured.

In another example relating to Behavior A′, Behavior A′ may be definedsuch that QC assumption cannot be established between a CRS and a DMRS,but can be established between a specific CSI-RS resource index (e.g.,CSI-RS resource index 0) and the DMRS. Behavior A′ defined as above issimilar to Behavior B. However, according to Behavior B, a CSI-RSresource which can be assumed to be QC with the DMRS is dynamicallyindicated through the DCI. According to Behavior A′, on the other hand,a CSI-RS to which QC assumption with the DMRS is applicable may besemi-statically indicated through RRC signaling or a specific CSI-RSresource index (e.g., CSI-RS resource index 0) may be staticallyconfigured.

In the various examples of Behavior A′ described above, the specificCSI-RS resource index (e.g., CSI-RS resource index 0) may be dynamicallyindicated as in Behavior B, rather than being statically orsemi-statically configured. For example, a CSI-RS port belonging to aCSI-RS resource (or a CSI process) to which QC assumption with the DMRSport is applicable may be indicated through a specific field of DCIformat 1A detected in an MBSFN subframe (or a UE-specific search spaceof the MBSFN subframe). In this case, Behavior B may be applied in botha case in which the DL grant is received through DCI format 1A in theMBSFN subframe and a case in which the DL grant is received through DCIformat 2D. Alternatively, Behavior A may be applied in a case in whichthe DL grant is received through DCI format 1A in the MBSFN subframe anda case in which TMs having indexes lower than that of TM9 (and in thiscase, the CSI-RS resource may be subject to semi-static RRC signaling ora specific CSI-RS resource index may be statically applied), whileBehavior B may be applied only in a case in which the DL grant isreceived through DCI format 2D.

Meanwhile, the CSI-RS may be excluded from definition of Behavior A.That is, Behavior A may be defined to assume that a CRS and a PDSCH DMRSare QC with respect to at least one of frequency shift, Doppler spread,received timing, and delay spread. Excluding QC assumption for theCSI-RS is intended to support a case such as CoMP scenario 4 in whichCRSs are simultaneously transmitted from multiple TPs in the form ofSFN, but CSI-RSs are not simultaneously transmitted from the TPs in theform of SFN. In other words, in Behavior A, estimates of large-scaleproperties which can aid in performing data demodulation can besufficiently reflected through QC assumption between the CRS and theDMRS alone, and channel properties measured using the CSI-RS having alower density than the CRS may not be viewed as greatly improving theperformance of DMRS-based data demodulation. For this reason, QCassumption between the CSI-RS and the DMRS may be excluded.

Further, Behavior A excluding the CSI-RS as above may be applied to acase in which no CSI-RS resource is configured for the UE (namely, a TDDsystem, a reciprocity system, and the like). On the other hand, if aCSI-RS resource is configured for the UE, QC assumptions among the CRS,the CSI-RS and the DMRS may be applied according to Behavior A describedabove. Behavior A may be restricted to be applied to only specific TM(s)(e.g., TM1 to TM9 or TM1 to TM8).

Behavior A depending on whether or not a CSI-RS resource is configuredmay be expressed as follows. Behavior A may be defined to assume that aCRS, a CSI-RS (if configured), and a PDSCH DMRS are QC with respect toat least one of frequency shift, Doppler spread, received timing anddelay spread. In other words, by assigning a condition of “ifconfigured” to the CSI-RS, Behavior A depending on whether or not theCSI-RS resource is configured may be briefly expressed.

Further, when details of Behavior A′ are incorporated into Behavior A,Behavior A may be defined as the following. Behavior A may be defined asa behavior of assuming that a CRS, a CSI-RS (if only one CSI-RS resourceis configured) and a PDSCH DMRS are QC with respect to at least one offrequency shift, Doppler spread, received timing and delay spread. Inother words, Behavior A may be defined as a behavior of assuming that aCRS, a CSI-RS (if the CSI-RS is configured, and the number of configuredCSI-RS resources is 1) and a PDSCH DMRS are QC with respect to at leastone of frequency shift, Doppler spread, received timing and delayspread. In other words, Behavior A may be defined as a behavior ofassuming that a CRS, a CSI-RS (if the CSI-RS is configured, the numberof configured CSI-RS resource is 1 (or UE capability P for the maximumnumber of CSI processes is {1})) and a PDSCH DMRS are QC with respect toat least one of frequency shift, Doppler spread, received timing anddelay spread.

By assigning a condition having the same meaning as “if one CSI-RSresource is configured” to the CSI-RS as above, Behavior A depending onwhether or not the CSI-RS resource is configured may be brieflyexpressed. Accordingly, when one CSI-RS resource is configured for theUE, QC assumption may be established among the CRS, the CSI-RS and theDMRS. If no CSI-RS resource is configured for the UE (as in, forexample, the TDD system), or two or more CSI-RS resources are configuredfor the UE (as in the case of, for example, TM10), QC assumption may beestablished only between the CRS and the DMRS, while QC assumption withthe CSI-RS is not applied.

If Behavior A is defined to include a case in which QC assumption isexcluded for the CSI-RS as above, Behavior A may also be applied to acase in which a DL grant is received through DCI format 1A in an MBSFNsubframe in TM10. Behavior B, on the other hand, may be applied only toa case in which the DL grant is received through DCI format 2D in TM10.

Among the proposed details above, QC Behavior of the UE in the case inwhich the DL grant is received through DCI format 1A in an MBSFNsubframe may also be applied to a case in which the DL grant is receivedthrough DCI format 1A in a non-MBSFN subframe (or only a case in whichthe DL grant is received through DCI format 1A in the UE-specific searchspace in a non-MBSFN subframe). This is because DMRS-based datademodulation can be defined as in the operation in an MBSFN subframe inthe case in which a DL grant is received through DCI format 1A in anon-MBSFN subframe in a new TM (e.g., TM10) (or through DCI format 1A inthe UE-specific search space in a non-MBSFN subframe) in a new system(e.g., a system after Rel-11), whereas CRS-based data demodulation isdefined in a legacy system (e.g., a system prior to Rel-10) such thatCRS-based data demodulation is performed when a DL grant is receivedthrough DCI format 1A in a non-MBSFN subframe. If DMRS (e.g., DMRS port7)-based data demodulation is defined, above descriptions of examples ofa case in which the DL grant is received through DCI format 1A in anMBSFN subframe may be applied to a case in which the DL grant isreceived through DCI format 1A in a non-MBSFN subframe.

Determination of PDSCH Symbol Location

In the examples of the present invention described above, descriptionhas been given of dynamically indicating information about whether ornot QC assumption is applied through an N bit field (e.g., a PQI field)in a DCI format and information associated with PDSCH RE mapping. Thepresent invention additionally proposes a method for additionallyindicating information associated with a PDSCH start symbol (or datastart symbol) (i.e., an OFDM symbol on which mapping of a PDSCH starts)through an N bit field in a DCI format.

Specifically, 2̂N parameter sets may be configured for the UE by a higherlayer, and one of the 2̂N parameter sets may be dynamically signaledthrough an N bit field (e.g., PQI field) in a DCI format. Herein,parameters in one parameter set may include PDSCH start symbolinformation.

It is assumed that OFDM symbol indexes of one subframe are given as 0,1, 2, . . . . That is, for a normal CP subframe, the OFDM symbol indexesof the first slot (or a slot having an even-numbered index if the slotindex begins with 0) are given as 0, 1, 2, 3, 4, 5, and 6, and the OFDMsymbol indexes of the second slot (or a slot having an odd-numberedindex if the slot index begins with 0) are given as 7, 8, 9, 10, 11, 12,and 13. For an extended CP, the OFDM symbol indexes of the first slot(or a slot having an even-numbered index) are given as 0, 1, 2, 3, 4,and 5, and the OFDM symbol indexes of the second slot (or a slot havingan odd-numbered index) are given as 6, 7, 8, 9, 10, and 11. In usualcases, a PDCCH may be mapped to OFDM symbol indexes from 0 to 1 or 2.The UE may recognize where the PDCCH symbol is through a PCFICH. Ifthere is not separate signaling of a PDSCH start symbol index, a symbolindex right next to the last PDCCH symbol index determined by the PCFICHis basically determined to be the PDSCH start symbol index.

In the present invention, a method of signaling PDSCH start symbolinformation is proposed separately from determination of the location ofa PDSCH start symbol based on the PCFICH (i.e., a CFI value). Forexample, the PDSCH start symbol information may be provided according toeach of 2̂N states indicated by an N bit field (e.g., a PQI field) in aDCI format indicating the QC assumption-associated information.Alternatively, PDSCH start symbol information to be applied to multiplestates of the 2̂N states in common may be configured through RRCsignaling.

The present invention proposes that the UE be informed of PDSCH startsymbol index information for each subframe pattern (or subframe set).There may be at least two subframe sets, and the UE may be pre-informedof configuration of the subframe sets. For example, one set includingMBSFN subframe(s) and another set including non-MBSFN subframe(s) may beconfigured. In this case, a PDSCH start symbol index applied to theMBSFN subframe and a PDSCH start symbol index applied to the non-MBSFNsubframe may be signaled respectively.

In another example, one PDSCH start symbol index value (e.g., index k)may be provided for each of 2̂N states indicated by an N bit field (e.g.,PQI field) in a DCI format (or as information commonly applied to allstates through separate RRC signaling). Further, a PDSCH start symbol isbasically determined according to the signaled value of k, but ifk>K_(Threshold), k=K_(Threshold) may be applied in a specific subframeset (e.g., an MBSFN subframe). That is, in a specific subframe, thesignaled k may be interpreted as having an upper limit (K_(Threshold)).In other words, k=min(K_(Threshold), K). Here, K is a PDSCH start symbolindex value applied to a normal subframe, and k is a PDSCH start symbolindex that the UE determines in the specific subframe.

The specific subframe set may be an MBSFN subframe or may be a non-MBSFNsubframe. In addition, the specific subframe set may represent onesubframe set or a plurality of subframe sets.

For example, if K_(Threshold)=3, it is assumed that a specific state ofan N bit field (e.g., a PQI field) in a DCI format indicates k=4. The UEperforms PDSCH demodulation considering that the PDSCH start symbolindex as signaled is 4 in a non-MBSFN subframe. In an MBSFN subframe,the UE interprets k as k=K_(Threshold)=3, thereby performing PDSCHdemodulation on the assumption that the PDSCH start symbol index is 3.Herein, K_(Threshold)=3 is but an example, and embodiments of thepresent invention are not limited thereto. K_(Threshold) may be 0, 1, 2,3, or 4.

To summarize the above proposal, the UE may determine, as a PDSCH startsymbol index value, one value (indicated by K) of values of RRC-signaledPDSCH start symbol candidates in a normal subframe (e.g., a non-MBSFNsubframe) a value determined from a PCFICH of a serving cell in the caseof non-cross-carrier scheduling, and a value set by a higher layer inthe case of cross-carrier scheduling. Herein, the values of RRC-signaledPDSCH start symbol candidates may be 0 or reserved values 1, 2, 3, and 4(4 is applied only when the system bandwidth corresponds to 10 or fewerPRBs). In a specific subframe (e.g., an MBSFN subframe), the PDSCH startsymbol index k of the specific subframe (e.g., the MBSFN subframe) isdetermined as k=min(K_(Threshold), K) (e.g., K_(Threshold)−2).

In another example, if the PDSCH start symbol determined as aboveoverlaps another control channel region (e.g., a DL serving cell controlchannel region), an OFDM symbol next to the control channel region maybe determined as the PDSCH start symbol.

For example, in a non-MBSFN subframe, the greater one of K and a value(i.e., P) determined from the PCFICH of the serving cell in the case ofnon-cross-scheduling or determined by a higher layer in the case ofcross-carrier scheduling may be determined as the PDSCH start symbol(i.e., k) (i.e., k=max{K, P}). Herein, K may be set to one of 0,reserved values of 1, 2, 3 and 4 (4 is applied only when the systembandwidth corresponds to 10 or fewer PRBs), a value determined from thePCFICH of a serving cell in the case of non-cross-carrier scheduling,and a value set by a higher layer in the case of cross-carrierscheduling. Meanwhile, in an MBSFN subframe indicated by the DCI, thegreater one of the least one of K_(Threshold) and K and P (i.e.,max{min(K_(Threshold), K), P}) may be determined as the PDSCH startsymbol (i.e., k).

In another example, the value of K may be determined regardless ofdetermining the PDSCH start symbol from the PCFICH of the serving cell.

For example, in a non-MBSFN subframe, the greater one of K and P may bedetermined as the PDSCH start symbol (i.e., k) (i.e., k=max{K, P}).Herein, K may be set to one of 0 and reserved values of 1, 2, 3 and 4 (4is applied only when the system bandwidth corresponds to 10 or lessPRBs). Meanwhile, in an MBSFN subframe indicated by the DCI, the greaterone of the at least one of K_(Threshold) and K and P (i.e.,max{min(K_(Threshold), K), P}) may be determined as the PDSCH startsymbol (i.e., k).

The method of determining the PDSCH start symbol as described above maybe limited not to be applied if the number of DwPTS symbols in theconfiguration of a special subframe in a TDD system is less than orequal to a specific value. 8 TDD special subframe configurations, forexample, may be defined. Of the TDD special subframe configurations,configurations having DwPTS symbols whose number is less than or equalto 3 may be configurations #0 and #5 (for details, see TS 36.211). Inother words, a rule relating to priority between a value determined forthe PDSCH start symbol information by RRC signaling and a valuedetermined by DCI signaling may be applied only to special TDDconfiguration(s) having symbols whose number exceeds a specific symbolnumber.

In another example, for a TDD system, TDD special configurations whichare scheduled to be applied to the 2̂N states for the DCI signalingrespectively may be signaled.

For example, independent TDD special subframe configuration(s) may beconfigured for each of 2̂N states by RRC signaling. Which of the 2̂Nstates should be applied to the currently scheduled PDSCH transmissionmay be dynamically indicated through DCI signaling. If a specific stateis indicated, and this state indicates a special subframe configuration(e.g., special subframe configuration 6), the UE may override anyspecial subframe configuration of the DL serving cell, and interpret theindicated special subframe configuration as meaning that a PDSCHcorresponding to the length of the OFDM symbol is transmitted in theDwPTS region according to the DCI-signaled special subframeconfiguration, thereby performing PDSCH demodulation according to theinterpretation.

If multiple special subframe configurations are indicated by the DCI, JTtransmission may be performed. This case may be interpreted as meaningthat there is always PDSCH transmission on a DwPTS symbol correspondingto an intersection of the special subframe configurations (namely, anOFDM symbol on which a DwPTS is present in the special subframeconfigurations in common) or that there is PDSCH transmission on a DwPTSsymbol corresponding to a union of the special subframe configurations(namely, an OFDM symbol according to a special subframe configurationhaving the largest DwPTS region among the special subframeconfigurations).

Additionally, PDSCH last symbol (PDSCH ending symbol, data last symbol,or data ending symbol) information may be explicitly signaled. In thiscase, the PDSCH last symbol information may be signaled together withthe special subframe configuration(s) according to the 2̂N states of theDCI signaling. Alternatively, only the last OFDM symbol information maybe signaled without signaling the special subframe configuration(s).

For example, the UE may determine a DwPTS region through the specialsubframe configuration(s) indicated through DCI signaling. Additionally,if PDSCH last OFDM symbol information is explicitly given, then the UEmay determine that a few OFDM symbol(s) in the last portion of the DwPTSregion are excluded from the PDSCH region, or more symbols may beincluded in the PDSCH region than in the DwPTS region. That is, givenPDSCH last OFDM symbol information, the UE may determine the PDSCHregion based on the PDSCH last OFDM symbol even if the special subframeconfigurations are given through DCI signaling.

Meanwhile, the UE may assume that special subframe configurations of aDL serving cell are applied and even PDSCH transmission from aneighboring cell/TP other than the serving cell matches the specialsubframe configurations of the serving cell, rather than signaling thespecial subframe configurations for 2̂N states indicated by an N bitfield (e.g., a PQI field) of a DCI format. In other words, it may bedefined that the UE can assume that the configurations are the same asthe special subframe configurations of the DL serving cell or that theUE is not allowed to expect that a special subframe configurationdifferent from the special subframe configurations of the DL servingcell will be provided. Similarly, if a PDSCH is scheduled in a DwPTS ofa special subframe, the UE is not allowed to expect that the PDSCH willbe transmitted from a cell/a TP other than the DL serving cell of theUE.

In another example, when a DL grant is transmitted in a special subframe(specifically, in a DwPTS), an N bit field (e.g., PQI field) may not beincluded in a corresponding DCI format. This may mean that a non-CoMPoperation is performed and that only PDSCH transmission from the DLserving cell may be scheduled in the special subframe.

In the various examples of the present invention described above, therange of the last OFDM symbol indexes of the DwPTS region may besignaled to the UE by informing the UE of the special subframeconfiguration(s) according to the 2̂N states of an N bit field (e.g., PQIfield) in the DCI format. In addition, signaling for determining a PDSCHstart OFDM symbol index may also be provided according to the 2̂N statesof the N bit field (e.g., a PQI field) in the DCI format by RRCsignaling. That is, information indicating the PDSCH start OFDM symbolindex and information about a TDD special subframe configuration fordetermining the PDSCH last OFDM symbol index may be included together inan RRC-configuration parameter set according to each of the 2̂N states.Thereby, the UE may determine the PDSCH start symbol and/or PDSCH lastsymbol included in a parameter set corresponding to a state valueindicated through DCI dynamic signaling, thereby correctly performingPDSCH demodulation.

Application of EPDCCH-Related PQI Parameter

QCL information about a DMRS and a CSI-RS, PDSCH RE mapping (or CRS RMpattern (e.g., the number of CRS ports, a CRS frequency shift, a cellidentifier, etc.)) information, information about MBSFN subframeconfigurations, NZP CSI-RS configuration information, zero-power (ZP)CSI-RS configuration information, TDD special subframe configurationinformation, PDSCH start symbol information, and/or PDSCH last symbolinformation may be defined by PQI parameters included in a parameter set(or a parameter list). Such parameter set may be referred to as a PQI(PDSCH RE mapping and QCL indicator) parameter set. Multiple (e.g., 2̂N)PQI parameter sets may be semi-statically configured by a higher layer.Of the 2̂N PQI parameter sets, a certain parameter set may be dynamicallyindicated by a state value of an N-bit PQI field (hereinafter, referredto as “PQI state value”) in a DCI format (e.g., DCI format 2D).

In addition, the information about the PQI parameter sets may besemi-statically configured in the form of a separate RRC-configuredparameter set, as information for the UE to depend on when theinformation is scheduled by DCI format 1A. Alternatively, a certain PQIparameter set may be configured as default information that the UEshould depend on in the case of DCI format 1A. A default PQI parameterset may be configured to, for example, match a configuration of aserving cell, or may be separately defined as a default configuration.The default PQI parameter set for DCI format 1A may be a parameter set(e.g., a parameter set corresponding to the least PQI state value (e.g.,‘00’)) (e.g., parameter set 1) of a plurality of PQI parameter setsconfigured for DCI format 2D by a higher layer.

Scheduling information corresponding to DCI format 1A may be signaled tothe UE over an EPDCCH. In the case of the EPDCCH, a specific PQIparameter set to be applied to each EPDCCH set may be configured byhigher layer signaling. The EPDCCH set (or EPDCCH-PRB-set) mayrepresent, for example, a localized EPDCCH mapping RB set or adistributed EPDCCH mapping RB set.

In the case in which scheduling information corresponding to DCI format1A is signaled to the UE through an EPDCCH, at least one of the PQIparameters may be pre-configured for each EPDCCH set by, for example,RRC signaling. Accordingly, the UE may operate according to some or allof parameters included in an RRC-configured parameter set configured for(or linked or mapped to) each EPDCCH set depending on an EPDCCH setthrough which DCI format 1A is transmitted to the UE. More specifically,the UE may perform blind decoding in a search space for eachpre-configured EPDCCH set, and if DCI format IA is successfully detectedas a result of blind decoding, the UE may perform reception processingby reflecting an assumption according to some or all of the parametersincluded in an RRC-configured parameter set linked to an EPDCCH setdescribing the search space in PDSCH demodulation scheduled by DCIformat 1A.

Causing the UE to operate according to the PQI parameters configured foreach EPDCCH set may be applied only when DCI format 1A is transmittedover the EPDCCH in TM10. If a plurality of EPDCCH sets is configured inTM10, a PQI parameter set may be RRC-configured for each EPDCCH set, andthe UE may reflect an assumption according to some or all of theparameters included in an RRC-configured parameter set corresponding toan EPDCCH set in PDSCH demodulation scheduled by DCI format 1A,depending on the EPDCCH set in which DCI format 1A has been detectedamong the EPDCCH sets. On the other hand, for TM1 to TM9, even if aplurality of EPDCCH sets is configured, some or all of the parametersincluded in the PQI parameter set may be configured to be applied to theEPDCCH sets in common. The UE may perform reception processing byreflecting an assumption according to some or all of the parametersincluded in the PQI parameter set and configured in common in PDSCHdemodulation scheduled by DCI format IA, regardless of the EPDCCH setthrough which DCI format 1A has been received and decoded.

While DCI format 1A has been given above as an example in describingembodiments of the present invention in which a PQI parameter set isRRC-configured EPDCCH set-specifically or EPDCCH set-commonly, theembodiments may also be applied to DCI format 2C or 2D.

In addition, a PQI parameter set for a DCI transmitted through alegacy-PDCCH and a PQI parameter set for a DCI transmitted through anEPDCCH may be independently RRC-configured. That is, they may bedifferent from each other since the PQI parameter set mapped to the PQIstate value of a DCI transmitted through a legacy-PDCCH is configuredindependently of the PQI parameter set mapped to the PQI state valuetransmitted through an EPDCCH.

An EPDCCH QC behavior may also be defined for each EPDCCH set. Forexample, RRC-configuration may be implemented such that EPDCCH BehaviorA or EPDCCH Behavior B is applied to each EPDCCH set. Herein, EPDCCHBehavior A is a behavior assuming a QCL relationship between an EPDCCHDMRS and a serving cell CRS. EPDCCH Behavior B is a behavior assuming aQCL relationship between the EPDCCH DMRS and a CSI-RS. Alternatively,EPDCCH Behavior A may be configured for all EPDCCH sets as a default QCbehavior, and EPDCCH Behavior B for a specific CSI-RS may beindependently configured for each EPDCCH set. The EPDCCH QC behaviorwill be separately described in detail later.

Further, not only a QCL behavior but also some or all of PQI parametersmay be configured for each EPDCCH set. In this case, some or all of theRRC-configured PQI parameter sets may be configured to be applied todecoding of the EPDCCH such that they correspond to 2̂N PQI state valuesof a DCI. For example, if a DCI (e.g., DCI format 2D) is transmittedthrough a legacy-PDCCH (or an EPDCCH), a PQI parameter set indicated bya specific state value among the PQI state values may be configured foreach EPDCCH set such that some or all of parameters of an RRC-configuredparameter set are applied to a specific EPDCCH set so as to correspondto the specific PQI state of the DCI.

In other words, a specific state value of the PQI state values may bedesignated for each EPDCCH set by RRC configuration. In addition, someor all of PQI parameters (QCL information about a DMRS and a CSI-RS,PDSCH RE mapping (or CRS RM pattern (e.g., the number of CRS ports, aCRS frequency shift, a cell identifier etc.)) information, informationabout an MBSFN subframe configuration, NZP CSI-RS configurationinformation, zero-power (ZP) CSI-RS configuration information, TDDspecial subframe configuration information, PDSCH start symbolinformation, and/or PDSCH last symbol information) indicated by thespecific PQI state value may be applied to EPDCCH decoding.

For example, RE mapping of the EPDCCH may be determined according to theZP CSI-RS configuration information, one of the PQI parameters, (on theassumption that the EPDCCH is not mapped to an RE indicated by the ZPCSI-RS), and the EPDCCH may be decoded.

Alternatively, RE mapping of the EPDCCH may be determined according tothe CRS RM pattern information, which is one of the PQI parameters, andthe EPDCCH may be decoded.

Alternatively, whether the subframe in which the EPDCCH is transmittedis an MBSFN subframe or non-MBSFN subframe may be determined accordingto the MBSFN subframe configuration information, which is one of the PQIparameters, and then whether or not there are RE(s) to which a CRS ismapped may be determined. Then, RE mapping of the EPDCCH may be finallydetermined, and the EPDCCH may be decoded.

Alternatively, a start symbol of the EPDCCH may be determined based onthe PDSCH start symbol information, which is one of the PQI parameters,to determine RE mapping of the EPDCCH and decode the EPDCCH. Forexample, k, the value of the PDSCH start symbol may be determined basedon the PDSCH start symbol information included in a PQI parameter set.The value of k may be used as the value of the start symbol of theEPDCCH. Herein, k indicating the start symbol index of the EPDCCH may beapplied to both an MBSFN subframe and a non-MBSFN subframe.Alternatively, k may be determined to be equal to K in the non-MBSFNsubframe, and be determined to be equal to min (K_(Threshold), K) in theMBSFN subframe. Herein, K may be set to one of 0, reserved values 1, 2,3 and 4 (4 is applied only when the system bandwidth corresponds to 10or fewer PRBs), a value determined from the PCFICH of a serving cell inthe case of non-cross-carrier scheduling, and a value set by a higherlayer in the case of cross-carrier scheduling. K_(Threshold) may be, forexample, 2.

When the PQI parameters include one piece of NZP CSI-RS configurationinformation, the NZP CSI-RS configuration information may be ignored (ormay not be considered) for decoding of the EPDCCH. Specifically, ifBehavior A or Behavior B is separately RRC-configured for each EPDCCHset, NZP CSI-RS configuration information included in the PQI parameterset for PDSCH demodulation is not applied to decoding of the EPDCCH.

Alternatively, NZP CSI-RS configuration information may be consideredfor a specific EPDCCH set indicated by EPDCCH Behavior B. The NZP CSI-RSconfiguration information may optionally be included in the PQIparameter set, and thus description will be given below of each case. Ifone NZP CSI-RS configuration is included in the PQI parameters, this maybe considered in determining RE mapping of the EPDCCH and decoding theEPDCCH. Specifically, if there is information about one NZP CSI-RSconfiguration belonging to an RRC-configured PQI parameter set for eachEPDCCH set, Behavior B assuming that the EPDCCH DMRS and the NZP CSI-RSare QCL is applied to decoding of the EPDCCH. If the configurationinformation about one NZP CSI-RS is not included in the PQI parameters,Behavior B assuming that the EPDCCH DMRS and a default CSI-RS are QCL isapplied to decoding of the EPDCCH. Herein, the default CSI-RS may be setto one of a CSI-RS resource assigned the lowest index (e.g., CSI-RSresource index 0), a specific CSI-RS resource (e.g., CSI-RS resourceindex n, where n has a predetermined value), a CSI-RS resource belongingto the lowest CSI process index (e.g., CSI process index 0) and a CSI-RSresource belonging to a specific CSI process (e.g., CSI process index n,where n has a predetermined value).

As described above, according to an embodiment of the present invention,a PQI parameter set configured for each of EPDCCH sets (or for allEPDCCH sets in common) by a higher layer may be used to determine REmapping and EPDCCH antenna port QCL of the EPDCCH. Thereby, theperformance of encoding the EPDCCH may be improved.

Priorities in Determining PDSCH Start Symbol

The N-bit PQI field in a DCI may have one of 2̂N PQI state values,thereby indicating one of 2̂N PQI parameter sets. The 2̂N PQI parametersets may be pre-configured by a higher layer (e.g., an RRC layer).

If a specific parameter is not included in a PQI parameter set, a valuedetermined according to a default rule may be applied for the specificparameter.

For example, if PDSCH start symbol index information is not included in(or given to) a PQI parameter set corresponding to the state value of aspecific PQI field, the UE may assume that the PDSCH start symbol indexmatches the PDSCH start location of the serving cell. This means thatthe UE determines that the location of an EPDCCH start symbol alreadygiven through RRC signaling is identical to the location of the PDSCHstart symbol rather than determining the PDSCH start symbol based on thePCFICH of the DL serving cell if an EPDCCH start symbol other than thePCI parameter is configured for the UE through separate RRC signaling inthe case in which the PDSCH start symbol is not included in the PQIparameters.

For example, if PDSCH start symbol index information is not included in(or given to) a PQI parameter set corresponding to the state value of aspecific PQI field, the UE may determine that the PDSCH start symbolindex is a symbol index next to the last symbol index of the PDCCHindicated by the PCFICH of the DL serving cell (namely, PDCCH lastsymbol index+1).

Priorities by which the PQI parameters proposed by the present inventionare applied are configured as follows. The first priority (i.e., anoperation that is applied first compared to the other cases) is tooperate according to a specific PQI parameter corresponding to a PQIstate value when the specific PQI parameter is given. The secondpriority (i.e., an operation that is applied when the operationaccording to the first priority is not applied), which is applied when aspecific PQI parameter corresponding to a PQI state value is not given,is to determine the value of the specific PQI parameter value accordingto a value, if given, that is separately configured (even for a purposeother than the PQI parameter configuration) in relation to the specificPQI parameter.

Hereinafter, an operation according to an embodiment of the presentinvention will be described in relation to the PDSCH start symbolinformation, which is one of the PQI parameters.

In order to determine whether to apply the operation according to thefirst priority or the operation according to the second priority, it isdetermined whether a PDSCH start symbol value is included in (or givento) a PQI parameter set corresponding to a specific state value of thePQI field in the DCI.

As the operation according to the first priority, if a PDSCH startsymbol value is provided by a PQI parameter set corresponding to aspecific state value of the PQI field in the DCI, the UE may performPDSCH demodulation (or EPDCCH decoding) using the PDSCH start symbolvalue.

Herein, PDSCH start symbol information (e.g., information represented byK in the above examples) that is RRC-signaled with respect to anon-MBSFN subframe may be one of 0, reserved values of 1, 2, 3 and 4 (4is applied only when the system bandwidth corresponds to 10 or lessPRBs), a value determined from the PCFICH of a serving cell in the caseof non-cross-carrier scheduling, and a value set by a higher layer inthe case of cross-carrier scheduling.

Alternatively, K may be set to one of 0, reserved values of 1, 2, 3 and4 (4 is applied only when the system bandwidth corresponds to 10 orfewer PRBs), a value determined from the PCFICH of a specific cell or TPin the case of non-cross-carrier scheduling, and a value set by a higherlayer in the case of cross-carrier scheduling. Herein, the method ofdynamically determining the number of PDSCH start symbols according tothe information (or another parameter/value/variable indicating thenumber of OFDM symbols in the control region) given by the PCFICH of thespecific cell or TP may be applied if an RE (e.g., CRS, CSI-RS, trackingRS, etc.) of the specific cell or TP can be reliably detected (by, forexample, a UE having an interference cancelation receiver).

The above operation of dynamically determining the PDSCH start symbol Kaccording to the PCFICH of a specific cell or TP may also be applied toother embodiments for preventing the DL control channel region and thePDSCH region from overlapping.

For example, in a non-MBSFN subframe, the PDSCH start symbol value k maybe determined to be max{K, P}. In an MBSFN subframe, the PDSCH startsymbol value k may be determined to be max{(min(K_(Threshold), K)).Herein, K may be set to one of 0, reserved values 1, 2, 3 and 4 (4 isapplied only when the system bandwidth corresponds to 10 or fewer PRBs),a value determined from the PCFICH of a specific cell or TP in the caseof non-cross-carrier scheduling, and a value set by a higher layer inthe case of cross-carrier scheduling. P may be set to a value determinedfrom the PCFICH of a serving cell in the case of non-cross-scheduling ora value set by a higher layer in the case of cross-carrier scheduling.K_(Threshold) may be, for example, 2.

As the operation according to the second priority, if a PDSCH startsymbol value is not provided by a PQI parameter set corresponding to aspecific state value of the PQI field in the DCI, but there is a PDSCHstart symbol value separately configured (even for a purpose other thanthe PQI parameter configuration), the UE may perform PDSCH demodulation(or EPDCCH decoding) using the separately configured value.

For example, the PDSCH start symbol configured separately from the PQIparameter may be information for indicating an EPDCCH start symbolvalue. In other words, it may be determined that EPDCCH startsymbol=PDSCH start symbol. To this end, if EPDCCH start symbolinformation is semi-statically configured in the UE, the UE maydetermine a PDSCH start symbol according to the information and performPDSCH demodulation.

As another example, even when the PDSCH start symbol information of theDL serving cell is not provided, the UE may perform PDSCH demodulationif there is PDSCH start symbol information configured for another cellor TP (e.g., a cell or TP which transmits a PDSCH through QC informationabout the CSI-RS). This may be interpreted as being similar to providingPDSCH start symbol information of an SCell through RRC signaling in acarrier aggregation (CA) system. Herein, the SCell may be viewed as aneighboring TP in a CoMP measurement set in the same frequency band.

For example, there may be a case in which DCI format 1A is used toperform fallback operation. In this case, information for an operationmode such as the CoMP mode (particularly, information about a PDSCHstart symbol) may not be provided. Alternatively, when a DCI forscheduling a PDSCH for the CoMP mode is given, if the DCI is transmittedin the common search space in which the UE attempts to detect ascheduling message together with other UEs, the DCI may not includePDSCH start symbol information in order to maintain the same length asthat of other scheduling information. If a PDSCH is scheduled byscheduling information not containing information about the PDSCH startsymbol as in this case, the EPDCCH and the PDSCH may have the same startpoint on the same cell (or CC).

As the operation according to the third priority, if no PQI parameter isgiven, nor is there a value configured for other purposes, the PDSCHstart symbol index may be determined to be a symbol index next to thelast symbol index of the PDCCH indicated by the PCFICH of the DL servingcell (namely, PDCCH last symbol index+1), as a method to support themost basic operation.

In another example, the greatest value which can be indicated by CFI ofthe PCFICH plus 1 (i.e., PDCCH maximum span+1) may be determined as thevalue of the PDSCH start symbol index. In the case of the method ofdetermining PDCCH maximum span+1 as the value of the PDSCH start symbolindex, resource availability may be degraded when the PDCCH uses fewersymbols than the maximum span. However, this method has an advantage ofsimplifying and stabilizing the operation of the UE. For example, thenumber of OFDM symbols which can be used for the PDCCH may be defined asshown in Table 10 below. In this case, when the downlink systembandwidth corresponds to 10 or fewer RBs (i.e., N_(RB) ^(DL)≦10), themaximum number of OFDM symbols for the PDCCH is 4. Accordingly, thePDSCH start symbol may be determined to be the 5th OFDM symbol (orsymbol index 4 when the OFDM symbol index starts from 0).

TABLE 10 Number of Number of OFDM OFDM symbols for symbols for PDCCHPDCCH when Subframe when N_(RB) ^(DL) > 10 N_(RB) ^(DL) ≦ 10 Subframes 1and 6 for frame 1, 2 2 structure type 2 MBSFN subframes on a carrier 1,2 2 supporting PDSCH, configured with 1 or 2 cell-specific antenna portsMBSFN subframes on a carrier 2 2 supporting PDSCH, configured with 4cell-specific antenna ports Subframes on a carrier not supporting 0 0PDSCH Non-MBSFN subframes (except 1, 2, 3 2, 3 subframe 6 for framestructure type 2) configured with positioning reference signals Allother cases 1, 2, 3 2, 3, 4

In another example, in Table 10, the greatest value may be determinedamong the values indicated by the CFI (namely, the number of OFDMsymbols) under given conditions such as a frame structure, whether asubframe is an MBSFN subframe or a non-MBSFN subframe, and the number ofCRS antenna ports, and a symbol index corresponding to the determinedgreatest value plus 1 may be determined as the position of the PDSCHstart symbol. The greatest value satisfying the above conditions may bedetermined to be the greatest value in a specific row or a specificcolumn in Table 10.

In another example, PDSCH start symbol position information of a cell orTP other than the DL serving cell may be used. For example, the cell orTP may be a cell or TP that transmits PDSCH according to QC informationabout a CSI-RS. When a specific signature value (e.g., a scrambling seedvalue such as a physical cell identifier and a virtual cell identifier)for the cell or TP is indicated, if the PCFICH can be decoded through anRS (e.g., a CRS, tracking RS, a CSI-RS, etc.) of the cell or TP, then asymbol index next to the last symbol index of the PDCCH determinedaccording to a CFI value indicated by the PCFICH may be determined to bethe location of the PDSCH start symbol.

In an additional example, if the UE receives specific PDSCH schedulinginformation (e.g., information about downlink scheduling through aspecific DCI format), a cell to transmit the PDSCH may be predeterminedto be a specific cell other than the serving cell of the UE. In thiscase, what the predetermined specific cell is may be configured by ahigher layer (e.g., the RRC layer).

If the PDSCH is scheduled by a DCI transmitted through the PDCCH ratherthan the EPDCCH, this may correspond to a case in which informationabout the EPDCCH start symbol is different from the information aboutthe PDSCH start symbol or there is no information about the EPDCCH startsymbol. In this case, the PDSCH start symbol value separately configuredin the second priority cannot be used, and therefore the location of thePDSCH start symbol may be determined according to the third priority.

Application of PQI Parameter to PDSCH Scheduled in Fallback Mode

When reconfiguration of the transmission mode is performed with respectto the UE, the operation mode of the eNB may be inconsistent with thatof the UE. In this case, both the UE and the eNB may operate in thefallback mode, which is basically supported, in order to ensure stableoperation. In this embodiment, it is proposed that a PQI parameter beapplied to a PDSCH scheduled in the fallback mode.

When operation is performed in the fallback mode, an operation accordingto the first priority (e.g., an operation performed in the case in whichthe PDSCH start symbol information is directly given) may not beapplied. Herein, when the UE and the eNB operate in the fallback mode,if the operation according to the first priority cannot be applied, anoperation according to the second priority (e.g., the operation ofdetermining the location of the PDSCH start symbol according to theEPDCCH start symbol information) may not be performed, but an operationaccording to the third priority (e.g., the operation of determining asymbol index next to the PDCCH last symbol index determined by a CFIvalue indicated by the PCFICH as the location of the PDSCH start symbol)may be performed.

For example, the start symbol location of PDSCH transmission scheduledby a DCI format for the fallback mode (e.g., DCI format 1A) may beconfigured to be different from that of the EPDCCH start symbol of thesame cell (CC) in order to ensure more stable fallback operation. Forexample, in the case in which a PDSCH is scheduled according to DCIformat 1A for the fallback mode, the PDSCH may be designated as a PDSCHtransmitted from a predetermined specific cell (e.g., a serving cell ofthe UE). This is because it is appropriate in the fallback mode to allowthe serving cell to manage operation of the UE. In this case, the startsymbol location of the PDSCH scheduled according to DCI format 1A ispreferably configured to be identical to the PDSCH start symbol locationof the serving cell.

Thereby, if the PDSCH is scheduled according to DCI format 1A, the UEmay determine the PDSCH start symbol location according to a valueindicated by the CFI of the PCFICH of the serving cell regardless of thestart symbol location of a separately RRC-configured EPDCCH.

Alternatively, PDSCH start symbol information of the serving cell may beprovided through higher layer signaling (e.g., RRC layer signaling) andoperation may be performed according to the information. Herein, thePDSCH start symbol information of the serving cell indicated by a higherlayer signal may be given as a PDSCH start symbol location to be appliedwhen the PDSCH is scheduled according to DCI format 1A or as a PDSCHstart symbol location to be used when the PDSCH can be assumed to betransmitted from the same location as that of a specific RS (e.g., a CRSor a specific reference CSI-RS) of the serving cell. Herein, thereference CSI-RS may be implicitly assumed to be transmitted by theserving cell, and correspond to a specific CSI-RS configuration indexsuch as the first (or lowest) CSI-RS configuration index.

In addition, even when a PDSCH scheduling message is detected in thecommon search space (CSS), and the information about the PDSCH startsymbol location is not contained in the PDSCH scheduling message,operation may be performed in a similar manner. In other words, in thecase of DCI format 1A transmitted in the CSS in a non-MBSFN subframe,CRS-based operation needs to be performed to provide the fallbackoperation that ensures the same operation in all transmission modes, itis preferable to ensure that the PDSCH start symbol location isdetermined according to the PCFICH information of the serving cell.

To summarize the above proposal, the operation of the UE according to afirst embodiment of the present invention relating to application of aPQI parameter in the fallback mode may be defined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A in the CSS in        a non-MBSFN subframe, the start symbol of the PDSCH is        determined based on PCFICH information (i.e., CFI) of the DL        serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in a        UE-specific search space in an MBSFN subframe or a non-MBSFN        subframe, the start symbol of the PDSCH is determined according        to a PQI parameter matching a predetermined one of PQI state        values configured for DCI format 2D. Herein, DCI format 2D        exemplarily refers to a DCI format including a PQI field. In        addition, the predetermined one of the PQI state values        represents a default PQI state value, and may be defined as, for        example, the first PQI state value or the lowest PQI state        value.

As a second embodiment of the present invention relating to applicationof a PQI parameter in the fallback mode, a UE operation may be definedso as to allow operation in the fallback mode even when a PDSCH isscheduled by a DCI transmitted in the UE-specific search space in anon-MBSFN subframe. Thereby, the UE operation may be defined for thecase of the MBSFN subframe and the non-MBSFN subframe as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A in a        non-MBSFN subframe, the start symbol of the PDSCH is determined        based on PCFICH information (i.e., CFI) of the DL serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in an MBSFN        subframe, the start symbol of the PDSCH is determined according        to a PQI parameter matching a predetermined one of PQI state        values configured for DCI format 2D. Herein, DCI format 2D        exemplarily refers to a DCI format including a PQI field. In        addition, the predetermined one of the PQI state values        represents a default PQI state value, and may be defined as, for        example, the first PQI state value or the least PQI state value.

It has been proposed, in the exemplary embodiments of the presentinvention described above, that the PDSCH start symbol should bedetermined based on PCFICH information (i.e., the CFI) of the servingcell when PDSCH demodulation is performed based on the CRS. In the caseof TM10, when a PDSCH is scheduled according to DCI format 1A in anon-MBSFN subframe as in the case of TM9, if CRS-based PDSCHtransmission (e.g., antenna port 0 transmission or transmit diversitymode) is performed regardless of whether DCI format 1A is detected inthe common search space or the UE-specific search space, the PQIparameter may not be applied as described above in the second embodimentof the present invention relating to application of the PQI parameter inthe fallback mode, but the PDSCH start symbol may be determined based onthe PCFICH information (i.e., the CFI) of the serving cell. Meanwhile,DCI format 1A transmitted through an EPDCCH in a non-MBSFN subframe istransmitted only in the UE-specific search space. Accordingly, asdescribed above in the first embodiment relating to application of a PQIparameter in the fallback mode, the PDSCH start symbol of a PDSCHscheduled according to DCI format 1A received through the common searchspace in a non-MBSFN subframe may be determined based on the PCFICHinformation (i.e., the CFI) of the serving cell, while a PQI parametercorresponding to a specific PQI state value may be applied to a PDSCHscheduled according to another DCI format 1A.

Regarding the first and second embodiments of the present inventionrelating to application of a PQI parameter in the fallback mode, UEoperations according to an additional embodiment performed depending onwhether DCI format 1A is transmitted over an EPDCCH or a PDCCH may bedefined as follows.

A variation of the first embodiment relating to application of a PQIparameter in the fallback mode may be defined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A transmitted        through an EPDCCH in the common search space in a non-MBSFN        subframe, the start symbol of the PDSCH is determined according        to the EPDCCH start symbol. Herein, the EPDCCH start symbol may        be determined based on the PCFICH information (i.e., the CFI) of        the serving cell, or determined according to an RRC-configured        EPDCCH start symbol value.    -   If a PDSCH is scheduled according to DCI format 1A transmitted        through a PDCCH in the common search space in a non-MBSFN        subframe, the start symbol of the PDSCH is determined based on        the PCFICH information (i.e., the CFI) of a DL serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in the        UE-specific search space in an MBSFN subframe or a non-MBSFN        subframe, the start symbol of the PDSCH is determined according        to a PQI parameter matching a predetermined one of PQI state        values configured for DCI format 2D, regardless of whether        transmission is performed through the PDCCH or the EPDCCH.        Herein, DCI format 2D exemplarily refers to a DCI format        including a PQI field. In addition, the predetermined one of the        PQI state values represents a default PQI state value, and may        be defined as, for example, the first PQI state value or the        lowest PQI state value.

A variation of the second embodiment relating to application of a PQIparameter in the fallback mode may be defined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A transmitted        through an EPDCCH in a non-MBSFN subframe, the start symbol of        the PDSCH is determined according to the EPDCCH start symbol.        Herein, the EPDCCH start symbol may be determined based on the        PCFICH information (i.e., the CFI) of the serving cell, or        determined according to an RRC-configured EPDCCH start symbol        value.    -   If a PDSCH is scheduled according to DCI format 1A transmitted        through a PDCCH in a non-MBSFN subframe, the start symbol of the        PDSCH is determined based on the PCFICH information (i.e., the        CFI) of a DL serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in an MBSFN        subframe, the start symbol of the PDSCH is determined according        to a PQI parameter matching a predetermined one of PQI state        values configured for DCI format 2D regardless of whether        transmission is performed through the PDCCH or the EPDCCH.        Herein, DCI format 2D exemplarily refers to a DCI format        including a PQI field. In addition, the predetermined one of the        PQI state values represents a default PQI state value, and may        be defined as, for example, the first PQI state value or the        lowest PQI state value.

The various embodiments of the present invention relating to a methodfor determining the PDSCH start symbol in the fallback mode (e.g., whenthe PDSCH is scheduled according to DCI format 1A) described above maybe similarly applied to the operation of determining a CRS RM (RateMatching) pattern (e.g., the number of CRS ports, CRS frequency shiftinformation, MBSFN configuration information, etc.). This serves toeliminate ambiguity and promote stability by determining the PDSCH startsymbol according to the PCFICH information (i.e., the CFI) of a servingcell in the case of CRS-based PDSCH transmission (e.g., antenna port 0transmission or transmit diversity mode) scheduled according to fallbackmode DCI format 1A. Accordingly, it is appropriate to determine PDSCH REmapping according to the CRS RM pattern of the serving cell for the samepurpose. That is, a PQI parameter (e.g., PDSCH start symbol information,CRS RM pattern, etc.) corresponding to a specific PQI state value (e.g.,the first PQI state value or the lowest PQI state value) configured forDCI format 2D is preferably applied only to PDSCH transmission (e.g.,DMRS-based PDSCH transmission) other than CRS-based PDSCH transmission(e.g., antenna port 0 transmission or transmit diversity mode). When theCRS RM pattern is determined in this way, PDSCH RE mapping may becorrespondingly determined.

Herein, demodulation of a PDSCH transmitted based on the CRS may beperformed using a part of the PQI parameter, and the other parametersmay match information of the serving cell. For example, only informationabout ZP CSI-RS configuration and/or PDSCH start symbol may be appliedto demodulation of the PDSCH transmitted based on the CRS among theparameters included in the PQI parameter set, and information about theCRS RM pattern may not be applied (namely, the CRS RM pattern may matchthe information of the serving cell). Corresponding UE operations may bedefined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A in the common        search space in a non-MBSFN subframe, the CRS RM pattern is        determined based on the CRS RM pattern information of the DL        serving cell. Herein, the CRS RM pattern information of the        serving cell may include, for example, the number of CRS ports        of the serving cell, CRS frequency shift of the serving cell,        and an MBSFN subframe configuration of the serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in the        UE-specific search space in an MBSFN subframe or a non-MBSFN        subframe, the CRS RM pattern is determined based on a parameter        associated with the CRS RM pattern among the PQI parameters        depending on a predetermined one of PQI state values configured        for DCI format 2D. Herein, DCI format 2D refers to a DCI format        including a PQI field. In addition, the predetermined one of the        PQI state values represents a default PQI state value, and may        be defined as, for example, the first PQI state value or the        lowest PQI state value. In addition, the parameter associated        with the CRS RM pattern among the PQI parameters corresponds to        the number of CRS ports (e.g., 1, 2, 4, or reserved value), CRS        frequency shift, and an MBSFN subframe configuration.

According to an embodiment of the present invention relating todetermination of the CRS RM pattern, in order to ensure operation in thefallback mode in the case in in which a PDSCH is scheduled according toDCI transmitted in the UE-specific search space in a non-MBSFN subframe,the following UE operations may be defined. Thereby, UE operations maybe defined separately according to the MBSFN subframe and the non-MBSFNsubframe respectively.

-   -   If a PDSCH is scheduled according to DCI format 1A in a        non-MBSFN subframe, the CRS RM pattern is determined based on        the CRS RM pattern information of the DL serving cell. Herein,        the CRS RM pattern information of the serving cell may include,        for example, the number of CRS ports of the serving cell, CRS        frequency shift of the serving cell, and an MBSFN subframe        configuration of the serving cell.    -   If a PDSCH is scheduled according to DCI format 1A in an MBSFN        subframe, the CRS RM pattern is determined based on a parameter        associated with the CRS RM pattern among the PQI parameters        depending on a predetermined one of PQI state values configured        for DCI format 2D. Herein, DCI format 2D exemplarily refers to a        DCI format including a PQI field. In addition, the predetermined        one of the PQI state values represents a default PQI state        value, and may be defined as, for example, the first PQI state        value or the lowest PQI state value. In addition, the parameter        associated with the CRS RM pattern among the PQI parameters        corresponds to the number of CRS ports (e.g., 1, 2, 4, or        reserved value), CRS frequency shift, and an MBSFN subframe        configuration.

According to a variation of the embodiment, regardless of the subframetype (e.g., MBSFN or non-MBSFN) and the search space type (e.g., commonsearch space or UE-specific search space), if a PDSCH is scheduledaccording to DCI format 1A, the UE may operate according to a PQIparameter corresponding to a predetermined one (e.g., the lowest PQIstate value) of the PQI state values configured for DCI format 2D. If aCRS-based PDSCH is scheduled, however, the UE may not be allowed toexpect that PDSCH start symbol information and/or CRS RM patterninformation, which are PQI parameters, will be RRC-configured accordingto information of a cell other than the serving cell. Corresponding UEoperations may be summarized as follows.

First, a UE operation for the CRS RM information may be defined asfollows.

-   -   If a PDSCH is scheduled according to DCI format 1A in a        non-MBSFN subframe, the UE is not allowed to expect that a        parameter associated with the CRS RM pattern indicated by a        predetermined one of the PQI state values configured for DCI        format 2D will differ from the CRS RM information of the serving        cell of the UE. Herein, DCI format 2D refers to a DCI format        including a PQI field. In addition, the predetermined one of the        PQI state values represents a default PQI state value, and may        be defined as, for example, the first PQI state value or the        lowest PQI state value. In addition, the parameter associated        with the CRS RM pattern among the PQI parameters corresponds to        the number of CRS ports (e.g., 1, 2, 4, or reserved value), CRS        frequency shift, and an MBSFN subframe configuration.

The above UE operation may be expressed as follows.

-   -   When the UE set to TM10 receives a PDSCH demodulated through        ports 0 to 3, the UE may assume that the number of CRS ports in        a PQI state defining RE mapping of the PDSCH, v-shift (or        frequency shift), and MBSFN subframe configuration information        as given are identical to those of the serving cell. Herein,        ports 0 to 3 represent CRS antenna port indexes.

Next, a UE operation for the PDSCH start symbol information may bedefined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A in a        non-MBSFN subframe, the UE is not allowed to expect that PDSCH        start symbol information indicated by a predetermined one of the        PQI state values configured for DCI format 2D will differ from        the PDSCH start symbol information of the serving cell of the        UE. Herein, DCI format 2D refers to a DCI format including a PQI        field. In addition, the predetermined one of the PQI state        values represents a default PQI state value, and may be defined        as, for example, the first PQI state value or the lowest PQI        state value.

The above UE operation may be expressed as follows.

-   -   When the UE set to TM10 receives a PDSCH demodulated through        ports 0 to 3, the UE may assume that the start symbol        information of a PQI state defining the start symbol of the        PDSCH as given is identical to that of the serving cell. Herein,        ports 0 to 3 represent CRS antenna port indexes.

According to another variation of the embodiment, if a PDSCH isscheduled according to DCI format 1A, the UE may operate according to aPQI parameter corresponding to a predetermined one (e.g., the lowest PQIstate value) of the PQI state values configured for DCI format 2D. If aPDSCH is scheduled according to DCI format 1A transmitted in the commonsearch space in a non-MBSFN subframe, the UE may not be allowed toexpect that PDSCH start symbol information and/or CRS RM patterninformation, which are PQI parameters, will be RRC-configured accordingto information of a cell other than the serving cell. Corresponding UEoperations may be summarized as follows.

First, a UE operation for the CRS RM information may be defined asfollows.

-   -   If a PDSCH is scheduled according to DCI format 1A in the common        search space in a non-MBSFN subframe, the UE is not allowed to        expect that a parameter associated with the CRS RM pattern        indicated by a predetermined one of the PQI state values        configured for DCI format 2D will differ from the CRS RM        information of the serving cell of the UE. Herein, DCI format 2D        refers to a DCI format including a PQI field. In addition, the        predetermined one of the PQI state values represents a default        PQI state value, and may be defined as, for example, the first        PQI state value or the lowest PQI state value. In addition, the        parameter associated with the CRS RM pattern among the PQI        parameters corresponds to the number of CRS ports (e.g., 1, 2,        4, or reserved value), CRS frequency shift, and an MBSFN        subframe configuration.

Next, a UE operation for the PDSCH start symbol information may bedefined as follows.

-   -   If a PDSCH is scheduled according to DCI format 1A in the common        search space in a non-MBSFN subframe, the UE is not allowed to        expect that PDSCH start symbol information indicated by a        predetermined one of the PQI state values configured for DCI        format 2D will differ from the PDSCH start symbol information of        the serving cell of the UE. Herein, DCI format 2D refers to a        DCI format including a PQI field. In addition, the predetermined        one of the PQI state values represents a default PQI state        value, and may be defined as, for example, the first PQI state        value or the lowest PQI state value.

PDSCH QCL Behavior and EPDCCH QCL Behavior

In the above description of various proposed embodiments of the presentinvention, Behavior A and Behavior B have been defined as QC behaviors(or PDSCH QCL behaviors) for a PDSCH. To summarize the behaviors, PDSCHQCL Behavior A is a behavior of assuming a QCL relationship among aserving cell CRS, a CSI-RS and a PDSCH DMRS, and PDSCH QCL Behavior B isa behavior of assuming a QCL relationship between a CSI-RS (e.g., aCSI-RS which is QCL with a CRS of a specific cell) and a PDSCH DMRS.

In the above description of various proposed embodiments of the presentinvention, Behavior A and Behavior B have been defined as QC behaviors(or EPDCCH QCL behaviors) for an EPDCCH. To summarize the behaviors,EPDCCH QCL Behavior A is a behavior of assuming a QCL relationshipbetween an EPDCCH DMRS and a serving cell CRS, and EPDCCH QCL Behavior Bis a behavior of a QCL relationship between an EPDCCH DMRS and a CSI-RS.

According to an additional embodiment of the present invention, EPDCCHQCL Behavior A and EPDCCH QCL Behavior B may be configured with arestriction depending on a PDSCH QCL behavior that is RRC-configured.

For example, if the UE is configured for PDSCH QCL Behavior A (i.e., QCLamong a serving cell CRS, a CSI-RS and a DMRS), EPDCCH QCL Behavior A(i.e., QCL between a serving cell CRS and an EPDCCH DMRS) may beautomatically configured. In other words, if the UE is configured forPDSCH QCL Behavior A, the EPDCCH QCL behavior should be configured onlyas EPDCCH QCL Behavior A. In other words, if the UE is configured forPDSCH QCL Behavior A, the UE is not allowed to expect that EPDCCH QCLBehavior B (i.e., QCL between a CSI-RS and an EPDCCH DMRS) will beconfigured. If the UE is configured for PDSCH QCL Behavior A,information about an NZP CSI-RS configuration intended for QCL may notbe included in the PQI parameters. Thereby, when EPDCCH QCL Behavior Bis configured, the UE cannot identify a CSI-RS with which the EPDCCHDMRS is QCL. Accordingly, if the UE is configured for PDSCH QCL BehaviorA, it is appropriate to configure EPDCCH QCL Behavior A in order toeliminate such ambiguity. For a similar purpose, when EPDCCH Behavior Ais configured, PDSCH Behavior A may be configured.

In another example, if the UE is configured for PDSCH QCL Behavior B(i.e., QCL between a CSI-RS and a DMRS), EPDCCH QCL Behavior B (i.e.,QCL between a CSI-RS and an EPDCCH DMRS) may be automaticallyconfigured. In other words, if the UE is configured for PDSCH QCLBehavior B, the EPDCCH QCL behavior should be configured only as EPDCCHQCL Behavior B. In other words, if the UE is configured for PDSCH QCLBehavior B, the UE is not allowed to expect that EPDCCH QCL Behavior A(i.e., QCL between the serving cell CRS and the EPDCCH DMRS) will beconfigured. This is intended to maintain unity of a PDSCH QCL behaviorand an EPDCCH QCL behavior. Similarly, if EPDCCH Behavior B isconfigured, PDSCH Behavior B may be configured.

In other words. restrictions may be applied such that both the PDSCH QCLbehavior and the EPDCCH QCL behavior are configured as QCL Behaviors Aor as QCL Behaviors B. That is, the PDSCH QCL behavior and the EPDCCHQCL behavior may be RRC-configured so as to be connected to or dependenton each other.

Meanwhile, if the UE is configured for PDSCH QCL Behavior B (i.e., QCLbetween a CSI-RS and a DMRS), the EPDCCH QCL behavior may be configuredas either EPDCCH QCL Behavior A ((i.e., QCL between a serving cell CRSand an EPDCCH DMRS) or EPDCCH QCL Behavior B (i.e., QCL between a CSI-RSand an EPDCCH DMRS). That is, only when the UE is configured for PDSCHQCL Behavior B, restrictions may be eased such that the EPDCCH QCLbehavior may be RRC-configured as EPDCCH QCL Behavior A or B.

Similarly, if EPDCCH QCL Behavior B is configured, one of PDSCH QCLBehaviors A and B may be configured.

Alternatively, the aforementioned restrictions may not be applied inorder to provide independency of configuration between the PDSCH QCLbehavior and the EPDCCH QCL behavior. Specifically, if the UE isconfigured for PDSCH QCL Behavior A (i.e., QCL among a serving cell CRS,a CSI-RS and a DMRS), the EPDCCH QCL Behavior may be configured aseither EPDCCH QCL Behavior A (i.e., QCL between a serving cell CRS andan EPDCCH DMRS) or EPDCCH QCL Behavior B (i.e., QCL between a CSI-RS andan EPDCCH DMRS).

Similarly, if EPDCCH QCL Behavior A is configured, the UE may beconfigured for one of PDSCH QCL Behaviors A and B.

Meanwhile, one specific PQI state value to be applied to each EPDCCH set(or to be used for demodulation of a PDSCH scheduled by DCI transmittedthrough an EPDCCH and/or for decoding of the EPDCCH) may beRRC-configured. In this case, if EPDCCH Behavior A (i.e., QCL between aserving cell CRS and an EPDCCH DMRS), the UE may operate according tosome of the PQI parameters included in a PQI parameter set linked to theone indicated specific PQI state value and to other PQI parameters ofthe DL serving cell, in order to perform PDSCH demodulation and/orEPDCCH decoding.

Herein, the PQI parameters included in a PQI parameter set linked to theone RRC-indicated specific PQI state value may include the number of CRSports, CRS frequency shift, MBSFN subframe configuration information,NZP CSI-RS configuration information, ZP CSI-RS configurationinformation, and PDSCH start symbol information.

For example, the UE may operate according to only the PDSCH start symbolinformation among the PQI parameters included in a PQI parameter setlinked to the one RRC-indicated specific PQI state value and to theother parameters of the serving cell.

In another example, the UE may operate according to only CRS RM patterninformation (e.g., the number of CRS ports of a serving cell, CRSfrequency shift of the serving cell, and MBSFN subframe configuration ofthe serving cell) among the PQI parameters included in a PQI parameterset linked to one RRC-indicated specific PQI state value and to theother parameters of the serving cell.

In yet another example, the UE may operate according to only ZP CSI-RSconfiguration information among the PQI parameters included in a PQIparameter set linked to one RRC-indicated specific PQI state value andto the other parameters of the serving cell.

In yet another example, the UE may operate according to only PDSCH startsymbol information and CRS RM pattern information (e.g., the number ofCRS ports of a serving cell, CRS frequency shift of the serving cell,and MBSFN subframe configuration of the serving cell) among the PQIparameters included in a PQI parameter set linked to one RRC-indicatedspecific PQI state value and to the other parameters of the servingcell.

In yet another example, the UE may operate according to only PDSCH startsymbol information and information of one ZP CSI-RS configuration amongthe PQI parameters included in a PQI parameter set linked to oneRRC-indicated specific PQI state value and to the other parameters ofthe serving cell.

In yet another example, the UE may operate according to only CRS RMpattern information (e.g., the number of CRS ports of a serving cell,CRS frequency shift of the serving cell, and MBSFN subframeconfiguration of the serving cell) and information of one ZP CSI-RSconfiguration among the PQI parameters included in a PQI parameter setlinked to one RRC-indicated specific PQI state value and to the otherparameters of the serving cell.

In yet another example, the UE may operate according to only PDSCH startsymbol information, CRS RM pattern information (e.g., the number of CRSports of a serving cell, CRS frequency shift of the serving cell, andMBSFN subframe configuration of the serving cell) and one ZP CSI-RSconfiguration information among the PQI parameters included in a PQIparameter set linked to one RRC-indicated specific PQI state value andto the other parameters of the serving cell.

Configuration of PQI Field

DCI format 2D for a new transmission mode (e.g., TM10) whose mainfeature is to support CoMP operation may include a PQI field. The PQIfield may be defined to have a size of N bits, thereby indicating one of2̂N state values. PQI parameter sets corresponding to the 2̂N PQI statevalues respectively may be RRC-configured. One PQI parameter set mayinclude the number of CRS ports, CRS frequency shift, MBSFN subframeconfiguration information, NZP CSI-RS configuration information, ZPCSI-RS configuration information, and PDSCH start symbol information.Accordingly, one of the 2̂N PQI parameter sets may be dynamicallyindicated or switched according to the PQI state value.

Meanwhile, DCI format 1A for the fallback operation in TM10 is definednot to include a PQI field. In other words, DCI format 1A in TM10without the PQI field means that a non-CoMP operation is supported byDCI format 1A, and may be interpreted as meaning that only non-CoMPtransmission from, for example, a DL serving cell is scheduled.

In another example, DCI format 1A transmitted in the common search spacemay be defined not to include the PQI field in order to maintain thesame length as that of the other DCI formats. On the other hand, DCIformat 1A transmitted in the UE-specific search space may be defined toinclude the PQI field as in the case of DCI format 2D, therebysupporting the CoMP operation.

In yet another example, DCI format 1A transmitted in a non-MBSFNsubframe may be defined not to include a PQI field, while DCI format 1Atransmitted in an MBSFN subframe may be defined to include the PQI fieldas in the case of DCI format 2D. Thereby, the CoMP operation may besupported.

In yet another example, DCI format 1A transmitted in the common searchspace in a non-MBSFN subframe may be defined not to include the PQIfield, while DCI format 1A transmitted in an MBSFN subframe and DCIformat 1A transmitted in the UE-specific search space in a non-MBSFNsubframe may be defined to include the PQI field as in the case of DCIformat 2D. Thereby, the CoMP operation may be supported.

In yet another example, DCI format 1A transmitted in a non-MBSFNsubframe and DCI format 1A transmitted in the common search space in anMBSFN subframe may be defined not to include a PQI field, while DCIformat 1A transmitted in the UE-specific search space in an MBSFNsubframe may be defined to include the PQI field as in the case of DCIformat 2D. Thereby, the CoMP operation may be supported.

Meanwhile, the PQI bit width (i.e., N) may be differently defineddepending on UE capabilities. For example, UE capability for the maximumnumber (N_P) of CSI processes supported (in TM10) may be defined, andthe UE may inform the eNB of the UE capability. For example, N_P may bedefined as N_P=1, 3, or 4.

According to one embodiment of the present invention, it is proposedthat the PQI bit width (N) be determined according to the value of N_P(N may be defined to indicate the PQI bit width, the number of PQIstates, an encoding pattern of PQI states, or the like).

If N_P=1, an explicit bit for the PQI may be defined as being notpresent in a DCI format. In this case, although there is no explicit bitfor the PQI, a PQI parameter set for one default PQI state may beRRC-signaled as default information, or RRC-configured parameterscorresponding to a default PQI state used in DCI format 1A may bedefined to be used in DCI format 2D without separate RRC signaling.

Alternatively, if N_P=1, an explicit bit for the PQI may not be defined,but 2 associated state values (0 or 1) may be used as PQI state valuesaccording to the value of the nSCID field.

Alternatively, if N_P=1, an explicit bit for the PQI may be included inthe DCI format. Thereby, 2 PQI state values may be provided.

If N_P=3 or 4, 2 explicit bits for the PQI may be defined to be includedin the DCI format.

Alternatively, if N_P=3 or 4, 1 explicit bit for the PQI may be includedin the DCI format, and 2 associated state values (0 and 1) may becombined according to the 1 bit and the value of the nSCID field toindicate one of 3 or 4 PQI states.

Alternatively, if N_P=3, only one explicit bit for the PQI may beapplied, and 2 state values may be restrictively used.

In the examples described above, PQI bit width (or the number of PQIstates) N is statically determined according to the UE capability valueN_P for the maximum number of supported CSI processes. Similarly, themaximum value of the PQI bit width (or the number of PQI states) may bedetermined according to the value of N_P. That is, a PQI parameter setmay be RRC-configured within the maximum value of the PQI bit width.

Meanwhile, RRC parameter set information of a PQI state to be used inDCI format 1A may be statically used for a specific PQI state (e.g., thelowest state index) of DCI format 2D. In addition, as a PQI parameter tobe used in the case of DCI format 1A, a PQI parameter indicated by aspecific PQI state of DCI format 2D may be RRC-configured.

FIG. 12 is a flowchart illustrating a method for transmitting andreceiving a EPDCCH signal according to one embodiment of the presentinvention.

In step S1210, PDSCH antenna port QCL may be configured for the UE by ahigher layer.

For example, the UE may be configured to decode the PDSCH based on afirst assumption or second assumption of PDSCH QCL. Herein, the firstassumption of PDSCH QCL may correspond to PDSCH QCL Behavior A (e.g., abehavior of assuming QCL of a CRS antenna port, a UE-specific RS for thePDSCH (or a DMRS for the PDSCH) and a CSI-RS). The second assumption ofPDSCH QCL may correspond to PDSCH QCL Behavior B (a behavior of assumingQCL of a UE-specific RS for the PDSCH (or a DMRS for the PDSCH) and aspecific CSI-RS).

In step S1220, the UE may determine the type of the EPDCCH antenna portQCL based on the type of PDSCH antenna port QCL (e.g., application ofthe first assumption or application of the second assumption).

For example, when the first assumption is applied to the PDSCH QCL, theUE is allowed to apply, to decoding of the EPDCCH, the assumption thatthe CRS antenna port and the EPDCCH DMRS antenna port are QCL. When thesecond assumption is applied to the PDSCH QCL, the UE is allowed toapply, to decoding of the EPDCCH, the assumption that the EPDCCH DMRSantenna port and the specific CSI-RS antenna port are QCL.

In step S1230, the UE may decode the EPDCCH based on the determinationof the EPDCCH QCL assumption. For example, large-scale properties of theEPDCCH DMRS may be inferred from the estimated/calculated large-scaleproperties of a port for another RS. Thereby, the EPDCCH may be decoded.

Once the UE succeed in decoding the EPDCCH, the UE may receive a PDSCHsignal allocated by the DCI transmitted through the EPDCCH.

Regarding the method of transmission and reception of the EPDCCH signaldescribed above with reference to FIG. 12, details of the variousembodiments of the present invention described above may beindependently applied or two or more embodiments may be simultaneouslyapplied. Redundant description is omitted.

FIG. 13 is a diagram illustrating configurations of a UE and an eNBaccording to one embodiment of the present invention.

Referring to FIG. 13, an eNB 10 may include a receive module 11, atransmit module 12, a processor 13, a memory 14, and a plurality ofantennas 15. The receive module 11 may receive various signals, data andinformation from external devices (e.g., a UE). The transmit module 12may transmit various signals, data and information to external devices(e.g., a UE). The processor 12 may control overall operation of the eNB10. The antennas 15 suggest that the eNB 10 supports MIMO transmissionand reception.

According to one embodiment of the present invention, the eNB 10 may beconfigured to transmit a PDSCH signal to the UE 20. The processor 13 mayprovide, to the UE 20, configuration of QCL assumption (e.g., Behavior Aor B) which the UE 20 needs to apply to decode the PDSCH, through higherlayer signaling. Thereby, the EPDCCH QCL assumption that the UE 20should apply to decode the EPDCCH may be determined. The processor 13may control the transmit module 12 to provide the UE 20 with the DCIthrough the EPDCCH and to transmit a PDSCH signal to the UE 20 asscheduled by the DCI.

Additionally, the processor 12 of the eNB 10 may function tooperationally process information received by the eNB 10 or informationto be transmitted from the eNB 10, and the memory 14, which may bereplaced with an element such as a buffer (not shown), may store theprocessed information for a predetermined time.

Referring to FIG. 13, a UE 20 may include a receive module 21, atransmit module 22, a processor 23, a memory 24, and a plurality ofantennas 25. The receive module 21 may receive various signals, data andinformation from external devices (e.g., an eNB). The transmit module 22may transmit various signals, data and information to external devices(e.g., an eNB). The processor 23 may control overall operation of the UE20. That there are plural antennas 25 suggests that the UE 20 supportsMIMO transmission and reception.

According to one embodiment of the present invention, the UE 20 may beconfigured to receive a PDSCH signal from the eNB 10. The processor 23may be configured to determine QCL with respect to an EPDCCH antennaport. The processor 23 may be configured to decode the EPDCCH based onthe QCL with respect to the EPDCCH antenna port. The processor 23 may beconfigured to decode the EPDCCH by applying the assumption of EPDCCH QCLbased on the PDSCH QCL type.

For example, when the first assumption of PDSCH QCL (e.g., an assumptionthat a CRS antenna port, a PDSCH UE-specific RS antenna port and aCSI-RS antenna port are QCL) is applied, the UE decode the EPDCCH on theassumption that the CRS antenna port and the antenna port for the EPDCCHDMRS are QCL.

When the second assumption of PDSCH QCL (e.g., an assumption that aPDSCH UE-specific RS antenna port and a specific CSI-RS antenna port areQCL) is applied, the UE decode the EPDCCH on the assumption that thespecific CSI-RS antenna port and the EPDCCH DMRS antenna port are QCL.

Additionally, the processor 23 of the UE 20 may function tooperationally process information received by the UE 20 or informationto be transmitted from the UE 20, and the memory 24, which may bereplaced with an element such as a buffer (not shown), may store theprocessed information for a predetermined time.

The configurations of the eNB 10 and the UE 20 as described above may beimplemented such that details of the various embodiments described aboveare independently applied or two or more embodiments are simultaneouslyapplied. Redundant description is omitted.

In describing the various embodiments of the present invention above,the eNB has been exemplarily described as serving as a downlink transmitentity or an uplink receive entity, and the UE has been exemplarilydescribed as serving as a downlink receive entity or an uplink transmitentity. However, embodiments of the present invention are not limitedthereto. For example, the description of the eNB given above may beequally applied to a case in which a cell, an antenna port, an antennaport group, an RRH, a transmission point, a reception point, an accesspoint, and a relay serve as a downlink transmit entity or an uplinkreceive entity with respect to the UE. In addition, the principle of thepresent invenition described above through various embodiments may beequally applied to a case in which a relay serves as a a downlinktransmit entity or an uplink receive entity with respect to the UE or toa case in wihch the relay serves as an uplink transmit entity or adownlink receive entity with respect to the eNB.

The embodiments of the present invention may be implemented throughvarious means, for example, hardware, firmware, software, or acombination thereof.

When implemented as hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented as firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to have the widest scope correspondingto the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended tohave the widest scope consistent with the principles and novel featuresdisclosed herein. In addition, claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention described above are applicableto various mobile communication systems.

1-13. (canceled)
 14. A method for transmitting an enhanced physicaldownlink control channel (EPDCCH) to a user equipment (UE) by a basestation in a wireless communication system, the method comprising:transmitting an indication indicating a first assumption or a secondassumption for decoding a physical downlink shared channel (PDSCH) tothe UE; and transmitting the EPDCCH to the UE, wherein the firstassumption indicates that antenna ports for a cell-specific referencesignal (CRS), a UE-specific reference signal (RS) for the physicaldownlink shared channel (PDSCH), and a channel state information-RS(CSI-RS) are quasi co-located, and wherein, when the indicationindicates the first assumption, the EPDCCH is decoded on an assumptionthat antenna ports for the CRS and a demodulation RS (DMRS) for theEPDCCH are quasi co-located.
 15. The method according to claim 14,wherein the second assumption indicates that antenna ports for theUE-specific RS for the PDSCH and a specific CSI-RS are quasi co-located,and wherein, when the indication indicates the second assumption, theEPDCCH is decoded on an assumption that antenna ports for the specificCSI-RS and the DMRS for the EPDCCH are quasi co-located.
 16. The methodaccording to claim 15, wherein, when the indication indicates the secondassumption, the specific CSI-RS is a non-zero power (NZP) CSI-RSconfigured by a higher layer.
 17. The method according to claim 14,wherein the indication is transmitted via higher layer signaling. 18.The method according to claim 14, wherein, when one antenna port andanother antenna port are quasi co-located, large-scale properties of theone antenna port are inferred from large-scale properties of the anotherantenna port.
 19. The method according to claim 18, wherein the largescale properties comprise at least one of delay spread, Doppler spread,Doppler shift and average delay.
 20. The method according to claim 14,wherein at least one EPDCCH-physical resource block (PRB)-set formonitoring the EPDCCH is configured for the UE, wherein a parameter setfor each of the at least one EPDCCH-PRB-set is indicated by a higherlayer, and wherein the EPDCCH is decoded based on the parameter set andthe indication.
 21. The method according to claim 20, wherein theparameter set is a specific PDSCH resource element mapping and Quasico-location Indicator (PQI) parameter set used for decoding the EPDCCH.22. The method according to claim 20, wherein the parameter setcomprises at least one of parameters corresponding to number-of-CRSports information, CRS frequency shift information, Multicast BroadcastSingle Frequency Network (MBSFN) subframe configuration information,zero power (ZP) CSI-RS configuration information, a PDSCH start symbolvalue, and non-zero power (NZP) CSI-RS configuration information. 23.The method according to claim 14, wherein a PDSCH signal is transmittedbased on downlink control information (DCI) transmitted through theEPDCCH.
 24. The method according to claim 14, wherein the UE is set totransmission mode 10 (TM10).
 25. A base station for transmitting anenhanced physical downlink control channel (EPDCCH) to a user equipment(UE) in a wireless communication system, the UE comprising: atransceiver; and a processor configured to control the transceiver,wherein the processor is further configured to: transmit an indicationindicating a first assumption or a second assumption for decoding aphysical downlink shared channel (PDSCH) to the UE, and transmit theEPDCCH to the UE, wherein the first assumption indicates that antennaports for a cell-specific reference signal (CRS), a UE-specificreference signal (RS) for the physical downlink shared channel (PDSCH),and a channel state information-RS (CSI-RS) are quasi co-located, andwherein, when the indication indicates the first assumption, the EPDCCHis decoded on an assumption that antenna ports for the CRS and ademodulation RS (DMRS) for the EPDCCH are quasi co-located.
 26. The basestation according to claim 25, wherein the second assumption indicatesthat antenna ports for the UE-specific RS for the PDSCH and a specificCSI-RS are quasi co-located, and wherein, when the indication indicatesthe second assumption, the EPDCCH is decoded on an assumption thatantenna ports for the specific CSI-RS and the DMRS for the EPDCCH arequasi co-located.
 27. The base station according to claim 26, wherein,when the indication indicates the second assumption, the specific CSI-RSis a non-zero power (NZP) CSI-RS configured by a higher layer.
 28. Thebase station according to claim 26, wherein at least one EPDCCH-physicalresource block (PRB)-set for monitoring the EPDCCH is configured for theUE, wherein a parameter set for each of the at least one EPDCCH-PRB-setis indicated by a higher layer, and wherein the EPDCCH is decoded basedon the parameter set and the indication.